Control of aerodynamic noise generated by high-performance jet engines continues to remain a serious problem for the aviation community. Intense low frequency noise produced by large-scale coherent structures is known to dominate acoustic radiation in the aft angles. A tremendous amount of research effort has been dedicated towards the investigation of many passive and active flow control strategies to attenuate jet noise, while keeping performance penalties to a minimum. Unsteady excitation,... Show moreControl of aerodynamic noise generated by high-performance jet engines continues to remain a serious problem for the aviation community. Intense low frequency noise produced by large-scale coherent structures is known to dominate acoustic radiation in the aft angles. A tremendous amount of research effort has been dedicated towards the investigation of many passive and active flow control strategies to attenuate jet noise, while keeping performance penalties to a minimum. Unsteady excitation, an active control technique, seeks to modify acoustic sources in the jet by leveraging the naturally-occurring flow instabilities in the shear layer. While excitation at a lower range of frequencies that scale with the dynamics of large-scale structures, has been attempted by a number of studies, effects at higher excitation frequencies remain severely unexplored. One of the major limitations stems from the lack of appropriate flow control devices that have sufficient dynamic response and/or control authority to be useful in turbulent flows, especially at higher speeds. To this end, the current study seeks to fulfill two main objectives. First, the design and characterization of two high-frequency fluidic actuators ($25$ and $60$ kHz) are undertaken, where the target frequencies are guided by the dynamics of high-speed free jets. Second, the influence of high-frequency forcing on the aeroacoustics of high-speed jets is explored in some detail by implementing the nominally 25 kHz actuator on a Mach 0.9 ($Re_D = 5\times10^5$) free jet flow field. Subsequently, these findings are directly compared to the results of steady microjet injection experiments performed in the same rig and to prior jet noise control studies, where available. Finally, limited acoustic measurements were also performed by implementing the nominally 25 kHz actuators on jets at higher Mach numbers, including shock containing jets, and elevated temperatures. Using lumped element modeling as an initial guide, the current work expands on the previous development of low-frequency (2-8 kHz) Resonance Enhanced Micro-actuators (REM) to design actuators that are capable of producing high amplitude pulses at much higher frequencies. Extensive benchtop characterization, using acoustic measurements as well as optical diagnostics using a high resolution micro-schlieren setup, is employed to characterize the flow properties and dynamic response of these actuators. The actuators produced high-amplitude output a range of frequencies, $20.3-27.8$ kHz and $54.8-78.2$ kHz, respectively. In addition to providing information on the actuator flow physics and performances at various operating conditions, the benchtop study serves to develop relatively easy-to-integrate, high-frequency actuators for active control of high-speed jets for noise reduction. Following actuator characterization studies, the nominally 25 kHz ($St_{DF} \approx 2.2$) actuators are implemented on a Mach 0.9 free jet flow field. Eight actuators are azimuthally distributed at the nozzle exit to excite the initial shear layer at frequencies that are approximately an order of magnitude higher compared to the \textit{jet preferred frequency}, $St_P \approx 0.2-0.3$. The influence of control on the mean and turbulent characteristics of the jet, especially the developing shear layer, is examined in great detail using planar and stereoscopic Particle Image Velocimetry (PIV). Examination of cross-stream velocity profiles revealed that actuation leads to strong, spatially coherent streamwise vortex pairs which in turn significantly modify the mean flow field, resulting in a prominently undulated shear layer. These vortices grow as they convect downstream, enhancing local entrainment and significantly thickening the initial shear layer. Azimuthal inhomogeneity introduced in the jet shear layer is also evident in the simultaneous redistribution and reduction of peak turbulent fluctuations in the cross-plane near the nozzle exit. Further downstream, control results in a global suppression of turbulence intensities for all axial locations, also evidenced by a longer potential core and overall reduced jet spreading. The resulting impact on the noise signature is estimated via far-field acoustic measurements. Noise reduction was observed at low to moderate frequencies for all observation angles. Direct comparison of these results with that of steady microjet injection revealed some notable differences in the initial development of streamwise vorticity and the redistribution of peak turbulence in the azimuthal direction. However, despite significant differences in the near nozzle aerodynamics, the downstream evolution of the jet appeared to approach near similar conditions with both high-frequency and steady microjet injection. Moreover, the impact on far-field noise was also comparable between the two injection methods as well as with others reported in the literature. Finally, for jets at higher Mach numbers and elevated temperatures, the effect of control was observed to vary with jet conditions. While the impact of the two control mechanisms were fairly comparable on non-shock containing jets, high-frequency forcing was observed to produce significantly larger reductions in screech and broadband shock-associated noise (BBSN) at select under-expanded jet conditions. The observed variations in control effects at different jet conditions call for further investigation. Show less

Supersonic impinging jets, similar to the jets issued from a short takeoff and vertical landing (STOVL) aircraft, generate a highly unsteady flow with high unsteady pressure and thermal loads on the aircraft structure as well as the landing surface. These high-pressure, high-temperature and acoustic loads are also accompanied by dramatic lift loss, severe ground erosion and hot gas ingestion in the engine inlets. Previous studies have concentrated on characterizing the impingement flow and... Show moreSupersonic impinging jets, similar to the jets issued from a short takeoff and vertical landing (STOVL) aircraft, generate a highly unsteady flow with high unsteady pressure and thermal loads on the aircraft structure as well as the landing surface. These high-pressure, high-temperature and acoustic loads are also accompanied by dramatic lift loss, severe ground erosion and hot gas ingestion in the engine inlets. Previous studies have concentrated on characterizing the impingement flow and its control for cold jets, i.e. operating at ambient temperatures. They have shown that one of the major characteristics of a supersonic impinging jet is the dominance of the feedback loop mechanism. Previous work has also shown that active microjet control is successful at attenuating the feedback loop and therefore the negative effects associated with it. The current studies attempt to examine and investigate the flow properties of a hot supersonic impinging jet issuing from a convergent-divergent, Mach 1.5 nozzle and operating at more realistic, higher temperatures,. This ideally expanded jet was heated up to a stagnation temperature of ~500K. The jet is impinging on a flat plate, called the ground plate that is appropriately larger than the nozzle exit diameter. The ground plate can be moved vertically in order to simulate different hover heights. In order to compare the properties of a cold and a heated impinging jet, mean pressure and unsteady pressure measurements, temperature measurements as well as acoustic measurements were obtained. The mean and unsteady pressure measurements as well as temperature measurements were performed on the lift plate (representing the undersurface of a STOVL aircraft) as well as on the ground plate. Acoustic near-field measurements were obtained using a microphone placed at 15-diameters away from the nozzle exit. Active microjet control was implemented as a way to attenuate the adverse effects of a jet impinging on a flat surface. It has already been shown that microjets are very effective when introduced to an impinging flow of a cold supersonic jet. Another aim of this study is to explore how effective microjet control is when the stagnation temperature of the primary jet is heated. The results clearly indicate that when the primary jet is heated, the pressure fluctuations and the associated unsteady loads, are substantially higher then when the jet is cold. These high unsteady loads also persist over larger nozzle to plate distances. The hover lift loss at high temperatures increases dramatically as well, from ~50% of the primary jet thrust at cold temperatures to an astounding ~75% of the primary jet thrust when the jet is heated. The temperature recovery factor is strongly dependent on the nozzle to plate distance and the temperature of the jet. There is an indication of an increase in entrainment of ambient air when the jet is heated. Additionally the unsteady thermal loads seem to increase in frequency as the stagnation temperature of the jet increases. These results show that the adverse side effects of an impinging supersonic jet are even more dramatic when the jet is at higher temperatures – a trend that is expected to continue as the temperatures are increased further to real jet exhaust conditions. However, this study also demonstrates that the activation of microjets can provide an effective way of reducing these negative effects even when the jet is heated. The pressure fluctuations have been drastically reduced, where the discrete impinging tones have been attenuated or even eliminated at both the cold and hot conditions. The overall pressure levels on the ground plane have been reduced up to 20dB and on the lift plate up to 15dB at small nozzle to ground plane distances while the jet was heated. Additionally up to 21% of the lift loss has been recovered at cold temperature jets and an astounding 35% of the lift loss was recovered when the jet is heated. The temperature recovery factor indicates a similar trend as the lift loss, which is that the entrainment of the ambient air is decreased when the microjets are applied. The thermal unsteady loads have been attenuated as well. In summary, this study demonstrates that the adverse effects of impinging supersonic jets are even more pronounced when the jet is heated, however microjet control is very effective at both cold and hot conditions. These dramatic reductions due to microjet control are achieved using microjets with a mass flow rate less than 0.5% of the primary jet flux. Show less

Date Issued

2008

Identifier

FSU_migr_etd-3217

Format

Thesis

Title

Active Control of Salient Flow Features in the Wake of a Ground Vehicle.

Aerodynamics of road vehicles have continued to be a topic of interest due the relationship between fuel efficiency and the environmental impact of passenger vehicles. With the streamlining of ground vehicles combined with years of geometric and shape optimization, other techniques are required to continue to improve upon fuel consumption. One such technique leverages aerodynamics to minimize drag through the implementation of flow control techniques. The current study focuses on the... Show moreAerodynamics of road vehicles have continued to be a topic of interest due the relationship between fuel efficiency and the environmental impact of passenger vehicles. With the streamlining of ground vehicles combined with years of geometric and shape optimization, other techniques are required to continue to improve upon fuel consumption. One such technique leverages aerodynamics to minimize drag through the implementation of flow control techniques. The current study focuses on the application of active flow control in ground vehicle applications, employing linear arrays of discrete microjets on the rear of a 25 Ahmed model. The locations of the arrays are selected to test the effectiveness of microjet control at directly manipulating the various features found in typical flow fields generated by ground vehicles. Parametric sweeps are conducted to investigate the flow response as a function of jet velocity, momentum, and vehicle scaling. The effect and effciency of the control are quantified through aerodynamic force measurements, while local modifications are investigated via particle image velocimetry and static pressure measurements on the rear surfaces of the model. Microjets proved most effective when utilized for separation control producing a maximum change to the coefficients of drag and lift of -14.0% and -42% of the baseline values, respectively. Control techniques targeting other flow structures such as the C-pillar vortices and trailing wake proved less effective, producing a maximum reduction in drag and lift of -1.2% and -7%. The change in the surface pressure distribution reveals the impact of each flow control strategy on a targeted flow structure, and highlights the complex interaction between the salient flow features found in the wake of the Ahmed model. Areas of pressure recovery on the surface of the model observed for each control technique support the observed changes to the aerodynamic forces. The time averaged, volumetric wake is also reconstructed to characterize the baseline flow field and highlight the effect of control on the three dimensional structure of the near wake region. The results show that separation control has a measurable effect on the flow field including modifications of the locations, size, magnitude, and trajectory of the various structures which comprise the near wake. The observations give insight into desirable modifications and flow topology which lead to an optimal drag configuration for a particular vehicle geometry. Show less

Date Issued

2018

Identifier

2018_Su_McNally_fsu_0071E_14507

Format

Thesis

Title

Active Control of Wingtip Vortices Using Piezoelectric Actuated Winglets.

Wingtip vortices develop at the tips of aircraft wings due to a pressure imbalance during the process of generating lift. These vortices significantly increase the total aerodynamic drag of an aircraft at high-lift flight conditions such as during take-off and landing. The long trailing vortices contain strong circulation and may induce rolling moments and lift losses on a trailing aircraft, making them a major cause for wake turbulence. A mandatory spacing between aircraft is administered by... Show moreWingtip vortices develop at the tips of aircraft wings due to a pressure imbalance during the process of generating lift. These vortices significantly increase the total aerodynamic drag of an aircraft at high-lift flight conditions such as during take-off and landing. The long trailing vortices contain strong circulation and may induce rolling moments and lift losses on a trailing aircraft, making them a major cause for wake turbulence. A mandatory spacing between aircraft is administered by civil aviation agencies to reduce the probability of hazardous wake encounters. These measures, while necessary, restrict the capacity of major airports and lead to higher wait times between take-off and landing of two aircraft. This poses a major challenge in the face of continuously increasing air traffic volume. Wingtip vortices are also known as a potent source of aerodynamic vibrations and noise. These negative effects have made the study of wingtip vortex attenuation a critical area of research. The problem of induced drag has been addressed with the development of wingtip device, like winglets. Tip devices diffuse the vortex at its very onset leading to lower induced drag. The problem of wake turbulence has been addressed in studies on vortex interactions and co-operative instabilities. These instabilities accelerate the process of vortex breakdown, leading to a lower lifetime in the wake. A few studies have tried to develop active mechanisms that can artificially excite these instabilities. The aim of the present study is to develop a device that can be used for both reducing induced drag and exciting wake instabilities. To accomplish this objective, an active winglet actuator has been developed with the help of piezoelectric Macro-Fiber Composite (MFC). The winglet is capable of oscillating about the main wing-section at desired frequency and amplitude. A passive winglet is a well-established drag reducing device. An oscillating winglet can introduce perturbations that can potentially lead to instabilities and accelerate the process of vortex breakdown. A half-body model of a generic aircraft configuration was fabricated to characterize and evaluate the performance of actuated winglets. Two winglet models having mean dihedral orientations of 0° and 75° were studied. The freestream velocity for these experiments was 20 m/s. The angle of incidence of the wing-section was varied between 0° and 8°. The Reynolds number based on the mid-chord length of the wing-section is 140000. The first part of the study consisted of a detailed structural characterization of the winglets at various input excitation and pressure loading conditions. The second part consisted of low speed wind tunnel tests to investigate the effects of actuation on the development of wingtip vortices at different angles of incidence. Measurements included static surface pressure distributions and Stereoscopic (ensemble and phase-locked) Particle Image Velocimetry (SPIV) at various downstream planes. Modal analysis of the fluctuations existing in the baseline vortex and those introduced by actuation is conducted with the help of Proper Orthogonal Decomposition (POD) technique. The winglet oscillations show bi-modal behavior for both structural and actuation modes of resonance. The oscillatory amplitude at these actuation modes increases linearly with the magnitude of excitation. During wind tunnel tests, fluid structure interactions lead to structural vibrations of the wing. The effect of these vibrations on the winglet oscillations decreases with the increase in the strength of actuation. At high input excitation, the actuated winglet is capable of generating controlled oscillations suitable for perturbing the vortex. The vortex associated with a winglet is stretched along its axis with multiple vorticity peaks. The center of the vortex core is seen at the root of the winglet while the highest vorticity levels are observed at the tip. The vortex core rotates and becomes more circular in shape while diffusing downstream. The shape, position, and strength of the vorticity peaks are found to vary periodically with winglet oscillation. Actuation is even capable of disintegrating the single vortex core into two vortices. The most energetic POD fluctuation modes, at the center of the baseline vortex core, correspond to vortex wandering at the initial downstream planes. At the farthest planes, the most energetic modes can be associated with core deformation. High energy fluctuations in the actuated vortex correspond to spatial oscillations and distortions produced by the winglet motion. Show less

Date Issued

2017

Identifier

FSU_SUMMER2017_Guha_fsu_0071E_14000

Format

Thesis

Title

Active Flow Control and Global Stability Analysis of Separated Flow over a NACA 0012 Airfoil.

The objective of this computational study is to examine and quantify the influence of fundamental flow control inputs in suppressing flow separation over a canonical airfoil. Most flow control studies to this date have relied on the development of actuator technology, and described the control input based on specific actuators. Taking advantage of a computational framework, we generalize the inputs to fundamental perturbations without restricting inputs to a particular actuator. Utilizing... Show moreThe objective of this computational study is to examine and quantify the influence of fundamental flow control inputs in suppressing flow separation over a canonical airfoil. Most flow control studies to this date have relied on the development of actuator technology, and described the control input based on specific actuators. Taking advantage of a computational framework, we generalize the inputs to fundamental perturbations without restricting inputs to a particular actuator. Utilizing this viewpoint, generalized control inputs aim to aid in the quantification and support the design of separation control techniques. This study in particular independently introduces wall-normal momentum and angular momentum to the separated flow using swirling jets through model boundary conditions. The response of the flow field and the surface vorticity fluxes to various combinations of actuation inputs are examined in detail. By closely studying different variables, the influence of the wall-normal and angular momentum injections on separated flow is identified. As an example, open-loop control of fully separated, incompressible flow over a NACA 0012 airfoil at α = 6° and $9° with Re = 23,000 is examined with large-eddy simulations. For the shallow angle of attack α = 6°, the small recirculation region is primarily affected by wall-normal momentum injection. For a larger separation region at α = 9°, it is observed that the addition of angular momentum input to wall-normal momentum injection enhances the suppression of flow separation. Reducing the size of the separated flow region significantly impacts the forces, and in particular reduces drag and increases lift on the airfoil. It was found that the influence of flow control on the small recirculation region (α = 6°) can be sufficiently quantified with the traditional coefficient of momentum. At α = 9°, the effects of wall-normal and angular momentum inputs are captured by modifying the standard definition of the coefficient of momentum, which successfully characterizes suppression of separation and lift enhancement. The effect of angular momentum is incorporated into the modified coefficient of momentum by introducing a characteristic swirling jet velocity based on the non-dimensional swirl number. With the modified coefficient of momentum, this single value is able to categorize controlled flows into separated, transitional, and attached flows. With inadequate control input (separated flow regime), lift decreased compared to the baseline flow. Increasing the modified coefficient of momentum, flow transitions from separated to attached and accordingly results in improved aerodynamic forces. Modifying the spanwise spacing, it is shown that the minimum modified coefficient of momentum input required to begin transitioning the flow is dependent on actuator spacing. The growth (or decay) of perturbations can facilitate or inhibit the influence of flow control inputs. Biglobal stability analysis is considered to further analyze the behavior of control inputs on separated flow over a symmetric airfoil. Assuming a spanwise periodic waveform for the perturbations, the eigenvalues and eigenvectors about a base flow are solved to understand the influence of spanwise variation on the development of the flow. Two algorithms are developed and validated to solve for the eigenvalues of the flow: an algebraic eigenvalue solver (matrix based) and a time-stepping algorithm. The matrix based approach is formulated without ever storing the matrices, creating a computationally memory efficient algorithm. Based on the matrix based solver, eigenvalues and eigenvectors are identified for flow over a NACA 0015 airfoil at Re = 200, $600, and $1,000. All three cases contain similar modes, although the growth rate of the leading eigenvalue is decreased with increasing Reynolds number. Three distinct types of modes are found, wake mode, steady mode, and modes of the continuous branch. While this method is limited in the range of Reynolds numbers, these results are used to validate the time-stepper approach. Increasing the Reynolds number to Re = 23,000 over a NACA 0012 airfoil, the time-stepper method is implemented due to rising computational cost of the matrix-based method. Stability analysis about the time-averaged flow is performed for spanwise wavenumbers of β = 1$, $10π, and $20π, which the latter two wavenumbers are representative of the spanwise spacing between the actuators. The largest spanwise wavelength (β = 1$) contained unstable modes that ranged from low to high frequency, and a particular unstable low-frequency mode corresponding to a frequency observed in the lift forces of the baseline large-eddy simulation. For the larger spanwise wavenumbers, β = 10π ($L_z/c = 0.2$) and $20π ($L_z/c = 0.1$), low-frequency modes were damped and only modes with $f > 5$ were unstable. These results help us gain further insight into the influence of the flow control inputs. Flow control is not implemented in a manner to directly excite specific modes, but does dictate the spanwise wavelengths that can be generated. Comparing the unstable eigenmodes at these two spacings, the larger spanwise spacing ($\beta = 10\pi$) had a greater growth rate for the majority of the unstable modes. The smaller spanwise spacing ($\beta = 20\pi$) has only a single unstable mode with a growth rate an order of magnitude smaller than $\beta = 10\pi$. With the aid of the increased growth rate, perturbations to the flow with a wider spacing become more effective by interacting with natural modes of the flow. Taking advantage of these natural modes allows for decreased input for the wider spanwise spacing. In conclusion, it was shown that the influence of wall-normal and angular momentum inputs on fully separated flow can adequately be described by the modified coefficient of momentum. Through further analysis and the development of a biglobal stability solver, spanwise spacing effects observed in the flow control study can be explained. The findings from this study should aid in the development of more intelligently designed flow control strategies and provide guidance in the selection of flow control actuators. Show less

Autonomous navigation systems for mobile robots have been successfully deployed for a wide range of planar ground-based tasks. However, very few counterparts of the previous planar navigation systems were developed for three-dimensional (3-D) motion, which is needed for unmanned aerial vehicles (UAVs). Safe maneuvering in complex environments is a major challenge for UAVs. Future urban reconnaissance and search missions will require UAVs to autonomously navigate through cluttered urban spaces... Show moreAutonomous navigation systems for mobile robots have been successfully deployed for a wide range of planar ground-based tasks. However, very few counterparts of the previous planar navigation systems were developed for three-dimensional (3-D) motion, which is needed for unmanned aerial vehicles (UAVs). Safe maneuvering in complex environments is a major challenge for UAVs. Future urban reconnaissance and search missions will require UAVs to autonomously navigate through cluttered urban spaces. This research proposes two approaches for unmanned helicopter navigation in cluttered urban environments: a 3-D fuzzy behavioral approach and a 3-D vector field histogram (VFH) approach. Behavior-based control has been very successful for planar mobile robots navigation in unknown environments. A novel fuzzy behavioral scheme for navigating an unmanned helicopter in cluttered 3-D spaces is developed. The 3-D navigation problem is decomposed into several identical two-dimensional (2-D) navigation sub-problems, each of which is solved by using preference-based fuzzy behaviors. Due to the shortcomings of vector summation during the fusion of the 2-D sub-problems, instead of directly outputting steering sub-directions by their own defuzzification processes, the undefuzzified intermediate results of the sub-problems are fused to a 3-D solution region, representing degrees of preference for the robot movement. A new defuzzification algorithm that steers the robot by finding the centroid of a 3-D convex region of maximum volume in the 3-D solution region is developed. A fuzzy speed control system is also developed to ensure the efficiency and safety of the navigation. The VFH approach is very popular for planar mobile robots. A 3-D VFH approach to UAV navigation in cluttered urban environments is developed. A 3-D laser measurement system is used to obtain the obstacle distribution in this method. Instead of a 2-D Cartesian histogram grid as a world model, a 3-D spherical histogram mesh is applied. This 3-D histogram mesh is updated continuously with range data. The 3-D VFH method subsequently employs a two-stage data-reduction process in order to compute the desired control commands for the robot. In the first stage the 3-D histogram mesh is reduced to a 2-D polar histogram corresponding to all possible steering directions for the robot. In the second stage, a novel convex finding algorithm is applied to efficiently find candidate directions from the 2-D polar histogram. The most suitable sector within the candidates with the lowest value of a particular cost function is selected, and the steering of the robot is aligned with that direction. Substantial simulations have been carried out to demonstrate that the two algorithms proposed in this dissertation can smoothly and effectively guide an unmanned helicopter through unknown and cluttered urban environments. Comparison simulation results show that the 3-D VFH has the ability to travel shorter and smoother pathes at most of scenarios. However, the feature doesn't apply to the 2-D counterparts. The 2-D fuzzy behavioral method usually has a smoother path, but the 2-D VFH travels a shorter path in most of scenarios. Show less

High-speed impinging jets are often generated by the propulsive systems of aerospace launch vehicles and tactical aircraft. In many instances, the presence of these impinging jets creates a hazard for flight operations personnel due to the extremely high noise levels and unsteady loads produced by fluid-surface interaction. In order to effectively combat these issues, a fundamental understanding of the flow physics and dominant acoustic behavior is essential. There are inherent challenges in... Show moreHigh-speed impinging jets are often generated by the propulsive systems of aerospace launch vehicles and tactical aircraft. In many instances, the presence of these impinging jets creates a hazard for flight operations personnel due to the extremely high noise levels and unsteady loads produced by fluid-surface interaction. In order to effectively combat these issues, a fundamental understanding of the flow physics and dominant acoustic behavior is essential. There are inherent challenges in performing such investigations, especially with the need to simulate the flowfield under realistic operational conditions (temperature, Mach number, etc.) and in configurations that are relevant to full-scale application. A state-of-the-art high-temperature flow facility at Florida State University has provided a unique opportunity to experimentally investigate the high-speed impinging jet flowfield at application-relevant conditions. Accordingly, this manuscript reports the findings of several experimental studies on high-temperature supersonic impinging jets in multiple configurations. The overall objective of these studies is to characterize the complex relationship between the hydrodynamic and acoustic fields. A fundamental parametric investigation has been performed to document the flowfield and acoustic characteristics of an ideally-expanded supersonic air jet impinging onto a semi-infinite flat plate at ambient and heated jet conditions. The experimental program has been designed to span a widely-applicable geometric parameter space, and as such, an extensive database of the flow and acoustic fields has been developed for impingement distances in the range 1d to 12d, impingement angles in the range 45 degrees to 90 degrees, and jet stagnation temperatures from 289K to 811K (TTR=1.0 to 2.8). Measurements include point-wise mean and unsteady pressure on the impingement surface, time-resolved shadowgraphy of the flowfield, and fully three-dimensional near field acoustics. Aside from detailed documentation of the flow and acoustic fields, this work aims to develop a physical understanding of the noise sources generated by impingement. Correlation techniques are employed to localize and quantify the spatial extent of broadband noise sources in the near-impingement region and to characterize their frequency content. Additionally, discrete impingement tones are documented for normal and oblique incidence angles, and an empirical model of the tone frequencies has been developed using velocity data extracted from time-resolved shadowgraphy together with a simple modification to the conventional feedback formula to account for non-normal incidence. Two application-based studies have also been undertaken. In simulating a vertical take-off and landing aircraft in hover, the first study of a normally-impinging jet outfitted with lift-plate characterizes the flow-acoustic interaction between the high-temperature jet and the underside of an aircraft and documents the effectiveness of an active flow control technique known as `steady microjet injection' to mitigate high noise levels and unsteady phenomena. The second study is a detailed investigation of the jet blast deflector/carrier deck configuration aimed at gaining a better understanding of the noise field generated by a jet operating on a flight deck. The acoustic directionality and spectral characteristics are documented for a model-scale carrier deck with particular focus on locations that are pertinent to flight operations personnel. Show less

An experimental study was conducted to examine the aeroacoustic characteristics of supersonic twin jets and compare them to a single jet of equivalent area. Axisymmetric converging diverging nozzles having a fully expanded Mach number of 1.76 were operated at overexpanded and ideally expanded conditions. Planar velocity field measurements were made using Particle Image Velocimetry (PIV) at cold operating conditions. The results obtained show a decrease in potential core length for the twin... Show moreAn experimental study was conducted to examine the aeroacoustic characteristics of supersonic twin jets and compare them to a single jet of equivalent area. Axisymmetric converging diverging nozzles having a fully expanded Mach number of 1.76 were operated at overexpanded and ideally expanded conditions. Planar velocity field measurements were made using Particle Image Velocimetry (PIV) at cold operating conditions. The results obtained show a decrease in potential core length for the twin jets. The twin jets were found to merge earlier when they were canted. Lower turbulence levels were observed for the twin jets compared to a single jet. The turbulence in the inter nozzle region of the canted twin jets was significantly reduced due to increased jet interaction. Far-field noise measurements for the twin jets were made at two azimuthal angles and compared to a single jet of equivalent diameter. Noise measurements showed a reduction in OASPL for the twin jets at most of the polar angles measured, with a 2 dB reduction in peak radiation direction. The OASPL levels of the twin jets showed a strong dependence on the azimuthal angle. Broadband shock noise was observed to have shifted to higher frequencies. Acoustic shielding was observed at some sideline angles, which caused significant reduction in high frequency noise. Show less

Date Issued

2005

Identifier

FSU_migr_etd-0650

Format

Thesis

Title

An Aeroacoustic Characterization of a Multi-Element High-Lift Airfoil.

The leading edge slat of a high-lift system is known to be a large contributor to the overall radiated acoustic field from an aircraft during the approach phase of the flight path. This is due to the unsteady flow field generated in the slat-cove and near the leading edge of the main element. In an effort to understand the characteristics of the flow-induced source mechanisms, a suite of experimental measurements has been performed on a two-dimensional multi-element airfoil, namely, the MD... Show moreThe leading edge slat of a high-lift system is known to be a large contributor to the overall radiated acoustic field from an aircraft during the approach phase of the flight path. This is due to the unsteady flow field generated in the slat-cove and near the leading edge of the main element. In an effort to understand the characteristics of the flow-induced source mechanisms, a suite of experimental measurements has been performed on a two-dimensional multi-element airfoil, namely, the MD-30P30N. Particle image velocimetry provide mean flow field and turbulence statistics to illustrate the differences associated with a change in angle of attack. Phase-averaged quantities prove shear layer instabilities to be linked to narrowband peaks found in the acoustic spectrum. Unsteady surface pressure are also acquired, displaying strong narrowband peaks and large spanwise coherence at low angles of attack, whereas the spectrum becomes predominately broadband at high angles. Nonlinear frequency interaction is found to occur at low angles of attack, while being negligible at high angles. To localize and quantify the noise sources, phased microphone array measurements are per- formed on the two dimensional high-lift configuration. A Kevlar wall test section is utilized to allow the mean aerodynamic flow field to approach distributions similar to a free-air configuration, while still capable of measuring the far field acoustic signature. However, the inclusion of elastic porous sidewalls alters both aerodynamic and acoustic characteristics. Such effects are considered and accounted for. Integrated spectra from Delay and Sum and DAMAS beamforming effectively suppress background facility noise and additional noise generated at the tunnel wall/airfoil junction. Finally, temporally-resolved estimates of a low-dimensional representation of the velocity vector fields are obtained through the use of proper orthogonal decomposition and spectral linear stochastic estimation. An estimate of the pressure field is then extracted by Poissons equation. From this, Curles analogy projects the time-resolved pressure forces on the airfoil surface to further establish the connection between the dominating unsteady flow structures and the propagated noise. Show less

Carbon Nanotubes have been undergoing intensive research since their discovery in 1991. They have some excellent properties based on their unique chemical structure. The industry has been impatient to use them as reinforcement in various applications in order to fully tap their properties. However some issues such as poor dispersion, lack of orientation, cost and poor interfacing have been limiting their usage on a large scale. The main objective if this thesis is to find a method to process... Show moreCarbon Nanotubes have been undergoing intensive research since their discovery in 1991. They have some excellent properties based on their unique chemical structure. The industry has been impatient to use them as reinforcement in various applications in order to fully tap their properties. However some issues such as poor dispersion, lack of orientation, cost and poor interfacing have been limiting their usage on a large scale. The main objective if this thesis is to find a method to process carbon nanotubes as a good reinforcement by trying to align them using a magnetic field. Some studies have been studied previously in this regard. These methods however use either extensive equipment or are not effective enough to apply on a large scale. Out of various manufacturing methods of carbon nanotubes, HiPCO processed nanotubes are the most popular ones to date. These nanotubes were used and composites were formed using 0.15 wt% nanotubes in an epoxy polymer. A suitable hardener was used and curing was done at room temperature in presence of a magnetic field. This sample was compared to another sample manufactured similarly without any magnetic field. The alignment was observed using a TEM. The inherent Fe impurities in HiPCO manufactured nanotubes were optimally used to assist in alignment. Conductivity experiments were done on a comparative basis. The unaligned and aligned composites showed marked difference in the conductivity. This was done indirectly by checking for change in dielectric constant at varying temperature. SQUID analysis was done to check for the magnetic properties of carbon nanotubes as they contained Fe as the dominant impurity. Also X-ray diffraction studies done to check the properties of the epoxy used in making the composite were also discussed. Show less

The superfluid phase of helium-4, known as He~II, is predominantly used to cool low-temperature devices. It transfers heat by a unique thermally driven counterflow of its two constituents, a classical normal fluid and an inviscid superfluid devoid of entropy. It also has potential use for economical reproduction and study of high Reynolds number turbulent flow due to the extremely small kinematic viscosity and classical characteristics exhibited by mechanically driven flow. A number of... Show moreThe superfluid phase of helium-4, known as He~II, is predominantly used to cool low-temperature devices. It transfers heat by a unique thermally driven counterflow of its two constituents, a classical normal fluid and an inviscid superfluid devoid of entropy. It also has potential use for economical reproduction and study of high Reynolds number turbulent flow due to the extremely small kinematic viscosity and classical characteristics exhibited by mechanically driven flow. A number of diagnostic techniques have been applied in attempts to better understand the complex behavior of this fluid, but one of the most useful, flow visualization, remains challenging because of complex interactions between foreign tracer particles and the normal fluid, superfluid, and a tangle of quantized vortices that represents turbulence in the superfluid. An apparatus has been developed that enables application of flow visualization using particle tracking velocimetry (PTV) in conjunction with second sound attenuation, a mature technique for measuring quantized vortex line density, to both thermal counterflow and mechanically-driven towed-grid turbulence in He~II. A thermal counterflow data set covering a wide heat flux range and a number of different fluid temperatures has been analyzed using a new separation scheme for differentiating particles presumably entrained by the normal fluid ("G2") from those trapped on quantized vortices ("G1"). The results show that for lower heat flux, G2 particles move at the normal fluid velocity vn, but for higher heat flux all particles move at roughly vn/2 ("G3"). Probability density functions (PDFs) for G1 particle velocity vp are Gaussian curves with tails proportional to |vp|⁻³, which arise from observation of particles trapped on reconnecting vortices. A probable link between G1 velocity fluctuations and fluctuations of the local vortex line velocity has been established and used to provide the first experimental estimation of c₂, a parameter related to energy dissipation in He~II. Good agreement between the length of observed G2 tracks and a simple model for the mean free path of a particle traveling through the vortex tangle suggests that flow visualization may be an alternative to second sound attenuation for measurement of vortex line density in steady-state counterflow. Preliminary PTV and second sound data in decaying He~II towed-grid turbulence shows agreement with theoretical predictions, and enables reliable estimation of an effective kinematic viscosity and calculation of longitudinal and transverse structure functions, from which information about the energy spectrum evolution and intermittency enhancement can be obtained. Show less

The semi-autonomous vehicle known as the Experimental Unmanned Vehicle (XUV)was designed by the US Army to autonomously navigate over different types of terrain. The performance of autonomous navigation improves when the vehicle's control system takes into account the type of terrain on which the vehicle is traveling. For example, if the ground is covered with snow a reduction of acceleration is necessary to avoid wheel slip.Previous researchers have developed algorithms based on vision and... Show moreThe semi-autonomous vehicle known as the Experimental Unmanned Vehicle (XUV)was designed by the US Army to autonomously navigate over different types of terrain. The performance of autonomous navigation improves when the vehicle's control system takes into account the type of terrain on which the vehicle is traveling. For example, if the ground is covered with snow a reduction of acceleration is necessary to avoid wheel slip.Previous researchers have developed algorithms based on vision and digital signal processing (DSP) to categorize the traversability of the terrain. Others have used classical terramechanics equations to identify the key terrain parameters. This thesis presents a novel algorithm that uses the vehicle's internal sensors to qualitatively categorize the terrain type in real-time. The algorithm was successful in identifying gravel, packed dirt, and grass. Show less

A piezohydraulic active flow control actuator is developed using a 400 µm diameter micro jet that is capable of pulsing flow over a broad frequency range. The design of the piezohydraulic microjet is presented together with experimental results that demonstrate multiphysics system dynamic characteristics. The microjet actuator couples a piezoelectric stack actuator and a hydraulic circuit to amplify the stack actuator displacement to an amplitude that is necessary to throttle flow through the... Show moreA piezohydraulic active flow control actuator is developed using a 400 µm diameter micro jet that is capable of pulsing flow over a broad frequency range. The design of the piezohydraulic microjet is presented together with experimental results that demonstrate multiphysics system dynamic characteristics. The microjet actuator couples a piezoelectric stack actuator and a hydraulic circuit to amplify the stack actuator displacement to an amplitude that is necessary to throttle flow through the micro jet. Unsteady pressure measurements at the microjet exit are compared with the piezoelectric stack actuator displacement and voltage input to provide comparisons between internal electromechanical actuation and external pulsed flow behavior. High-speed micro-Schlieren imagery is also utilized to quantify the flow field. The results illustrate broadband supersonic pulsed microjet actuator performance using a piezohydraulic circuit. Show less

Date Issued

2011

Identifier

FSU_migr_etd-3985

Format

Thesis

Title

Characterization and Nanostructure Analysis of Electrodeposited CuInSe₂ Thin Film for Applications in Flexible Solar Cells.

A roll-to-roll fabrication concept for manufacturing cost-effective thin film solar cells was developed. The model involves a combination of electroless and electrolytic depositions, and in this work, Polymer film Kapton®, electroless nickel (Ni), copper indium diselenide (CuInSe2, referred to as CIS), and ZnO were used to demonstrate the feasibility of the proposed concept. Typical flexible solar cell consists of polymer substrate, back contact (BC) and photovoltaic layers. Polymer film... Show moreA roll-to-roll fabrication concept for manufacturing cost-effective thin film solar cells was developed. The model involves a combination of electroless and electrolytic depositions, and in this work, Polymer film Kapton®, electroless nickel (Ni), copper indium diselenide (CuInSe2, referred to as CIS), and ZnO were used to demonstrate the feasibility of the proposed concept. Typical flexible solar cell consists of polymer substrate, back contact (BC) and photovoltaic layers. Polymer film Kapton® was metallized with electroless Ni, which served as the BC. The ideal duration for the electroless Ni deposition was determined to be between 2 to 5 minutes. The product was heat treated at 245oC for 45 minutes. The photovoltaic layer (CIS) was plated onto the electroless Ni back contact at various potentials (–0.5V to –1.1V vs. Ag/AgCl), and at different electrolyte circulating rate (0.3ml/s to 6.2ml/s). The CIS were also deposited onto different roughness back contacts to study the effect of surface roughness on the deposition quality. The deposited CIS were subjected to heat treatment at 390oC up to 2 hours in argon furnace. The materials were characterized using Atomic Force Microscope (AFM), Environmental Scanning Electron Microscope (ESEM), Energy Dispersive X-Ray Spectroscopy (EDS), and X-ray Diffraction (XRD). The results provided the basis for studying the effects of deposition parameters on the quality of the thin film. The Ni produced by the electroless method used in this investigation was amorphous. Although annealing did not improve its crystallinity, it affected the nano-scale cluster packing and the roughness of the Ni. Deposition potentials and electrolyte transport properties were proven to influence the atomic composition and morphology of produced film, while the effects of back contact roughness was inconclusive. Indium was found to favor lower flow rates and lower deposition potentials. Stoichiometric composition of CuInSe2 was achieved with electrolyte recirculating rate of 1ml/s. The CIS crystallinity was improved by annealing. The major diffraction peaks were identified to be CIS (112), (220), and (116). The lattice parameter were found to be a= b=5.77Å, c=11.54Å. This work clearly demonstrated that electroless and electrolytic methods can be used to mass produce thin film for solar cells. Show less

Humans and terrestrial legged animals can travel with great degree of stability, agility and maneuverability over a large number of terrains such as gravel, grass, sand, rock, mud, snow, asphalt, river-beds and more. They can also perform many locomotive tasks elegantly and seemingly effortlessly, showing their rich structural and dynamic readiness in rejecting even large, rapid and unexpected disturbances. However, despite significant advances in the robotic legged locomotion field during... Show moreHumans and terrestrial legged animals can travel with great degree of stability, agility and maneuverability over a large number of terrains such as gravel, grass, sand, rock, mud, snow, asphalt, river-beds and more. They can also perform many locomotive tasks elegantly and seemingly effortlessly, showing their rich structural and dynamic readiness in rejecting even large, rapid and unexpected disturbances. However, despite significant advances in the robotic legged locomotion field during the last three decades since Raibert introduced the first self-balancing hopping robot, there are not yet any robots that can run over real outdoor rough terrains as humans and animals do. During rapid locomotion, animals seem to use passive mechanisms such as sprawled posture or tuned mechanical impedances to self-stabilize and reject unexpected disturbances before the neural reflexes take place. These mechanisms allow for immediate response to perturbations, and, in this way, humans and animals are able to move with great stability and maneuverability over various types of terrains. With the purpose of designing robotic legs with similar passive mechanisms that biological legged systems have embedded, the present work focuses on relating the robotic leg's passive properties to various running performance measures. In particular, curved legs are chosen for this study motivated by the exceptional running performance achieved by some autonomous robots and human amputees using this type of leg. The relevant aspects of running with this type of leg are characterized by using various reduced-order dynamical models. Then, by associating the design parameters of each model to the running performance, these parameters are optimized to obtain new curved leg designs. The results of the present work reveal that, in the presence of changes in the environmental conditions, the approach of mechanical impedance adaptation is a more effective and realistic strategy than the controller optimization method for stable and efficient running. In addition, this work shows that running with curved legs is more efficient and robust and can recover from perturbations more quickly than with straight legs. These results are justified by the richer running dynamics involved with curved legs than with straight legs such as variable passive compliance and variable rest length due to the rolling motion involved during stance. In essence, the results obtained in this work show the importance of (actively or passively) tuning the mechanical properties of the leg to achieve stable and efficient running. These approaches do not only apply to robotic platforms with curved legs but can be generalized for any robotic legged system. Show less

Date Issued

2011

Identifier

FSU_migr_etd-4936

Format

Thesis

Title

Characterization and Validation of an Anechoic Facility for High-Temperature Jet Noise Studies.

In response to the increasing demand for jet noise studies performed at realistic conditions, the Florida Center For Advanced Aero-Propulsion at Florida State University has recently brought online an upgraded Anechoic High-Temperature Jet Facility. The function of this facility is to accurately simulate and characterize the aeroacoustic properties of exhaust from jet engines at realistic temperatures and flow speeds. This new addition is a blow-down facility supplied by a 3500 kPa, 114 cubic... Show moreIn response to the increasing demand for jet noise studies performed at realistic conditions, the Florida Center For Advanced Aero-Propulsion at Florida State University has recently brought online an upgraded Anechoic High-Temperature Jet Facility. The function of this facility is to accurately simulate and characterize the aeroacoustic properties of exhaust from jet engines at realistic temperatures and flow speeds. This new addition is a blow-down facility supplied by a 3500 kPa, 114 cubic meter compressed dry air system and a sudden-expansion ethylene burner that is capable of producing ideally expanded jets up to Mach 2.6 and stagnation temperatures up to 1500 K. The jet exhausts into a fully anechoic chamber which is equipped to acquire acoustic and flow measurements including the temperature and pressure of the jet. The facility is capable of operating under free jet as well as in various impinging jet configurations pertinent to sea- and land-based aircraft, such as the F-35B. Compared to the original facility, the updated rig is capable of longer run times at higher temperatures. In this paper we demonstrate the facility's experimental capabilities and document jet aeroacoustic characteristics at various flow and temperature conditions. The anechoic chamber was characterized using ISO (3745:2003) guidelines and the lower cutoff frequency of the chamber was determined to be 315 Hz. Aeroacoustic properties of jets operating at subsonic conditions and supersonic Mach numbers ranging from 1.2 to 2.1 at temperatures of ~300 K to ~1300 K are documented. Where available, very good agreement was found when the present results were compared with data in the jet noise literature. Show less

Date Issued

2016

Identifier

FSU_FA2016_Craft_fsu_0071N_13535

Format

Thesis

Title

Characterization of a High-Lift, Supercritical Airfoil with Microjets.

Active flow control (AFC) has the potential for substantial performance gains and meeting the challenges of next-generation high-lift aircraft. High-lift wings employ multi-element trailing edge flaps during takeoff and landing. When the aircraft is at cruise speed, these flaps are not required and are retracted to reduce drag. These aircraft wings with high-lift mechanisms enhance the lift characteristics at slower speeds, but suffer due to the added weight of these deployment/retraction... Show moreActive flow control (AFC) has the potential for substantial performance gains and meeting the challenges of next-generation high-lift aircraft. High-lift wings employ multi-element trailing edge flaps during takeoff and landing. When the aircraft is at cruise speed, these flaps are not required and are retracted to reduce drag. These aircraft wings with high-lift mechanisms enhance the lift characteristics at slower speeds, but suffer due to the added weight of these deployment/retraction mechanisms. In the present study, we have investigated the effect of active flow control using microjets to enhance the performance of a two-dimensional high-lift supercritical airfoil with a simply hinged flap. The airfoil used in the study is the NASA Energy Efficient Transport (EET) and the wind-tunnel tests were conducted at a freestream velocity of 20 m/s. Two different scaled models were used corresponding to Reynolds numbers of 1.3 x 105 and 3.4 x 105. The experiments pertaining to the small scaled model were carried out with two angles of incidence of 0° and 4° at a constant flap deflection of 20°. For the large scale model, a constant angle of incidence of 0° and flap deflection angles of 20° and 30° were investigated. A range of microjet momentum ratios and microjet orientations were studied for both models. Particle Image Velocimetry was carried out to study the mean velocity field and the effect of microjet control at the flap region of the airfoil. For the first model, the baseline flow at both the angles of incidence separates at the hinge line and remain separated over the entire flap region. The size of the re-circulation region is found to gradually decrease with an increase in microjet momentum ratio. Microjets oriented normal to the airfoil surface were relatively more effective and successful in re-attaching the flow over the entire airfoil at both the angles of incidence. Experiments for the second model consisted of both Planar and Stereoscopic Particle Image Velocimetry. The baseline flow is separated over a third of the flap at 20° and over the entire flap at 30°. Microjets oriented at a more tangential angle are able to completely re-attach the flow at both flap angles. In general, active flow control using high-momentum microjets was very effective in eliminating/reducing flow separation, however, its effectiveness was dependent on the geometric and flow parameters. Show less

Wind-and-react coils using alumino-silicate insulated Bi2Sr2CaCu2Ox (Bi-2212) round wire consistently show reduced transport properties compared to short samples heat treated under identical conditions. To take full advantage of the Bi-2212 high field transport properties, in particular to maximize the performance of insert coils for high field magnets, this problem needs to be understood and solved. There are a number of potential reasons for degraded coil performance like inhomogeneous... Show moreWind-and-react coils using alumino-silicate insulated Bi2Sr2CaCu2Ox (Bi-2212) round wire consistently show reduced transport properties compared to short samples heat treated under identical conditions. To take full advantage of the Bi-2212 high field transport properties, in particular to maximize the performance of insert coils for high field magnets, this problem needs to be understood and solved. There are a number of potential reasons for degraded coil performance like inhomogeneous temperature distribution throughout the coil and insufficient oxygen penetration and diffusion into the coil during heat treatment. Each one of these or even a combination may result in a radial dependence of the superconducting properties within the coil. In this work, short conductor samples were systematically extracted from various locations of three heat treated Bi-2212 coils and the electromechanical properties of these samples are measured to create a position-sensitive map of the properties for each coil. Sample microstructures are also examined and correlated with the property measurements. Results show that there are radial variations within each coil, particularly of transport current properties. For two of the coils there was an improvement for the inner most layer compared to the remaining layers, which were fairly homogeneous. On the other hand, the third coil experienced a decrease in performance for the 5 inner most layers compared to the remaining layers. It was found that there was no variation in performance in the vertical direction of the coil. Additional properties measured included the transition temperature Tc, the Kramer field HK and remnant field analysis of the wire connectivity. The first two of these were found to be homogeneous throughout each of the coils, implying that the oxygen content and flux pinning of the conductor was independent of position in the coil. Remnant field measurements were conflicting; with the results for two coils supporting the trend seen in transport current properties, but not in the third case. Show less

Characterization of fluid with suspended nanoparticles in microchannels has been studied as a part of a microfluidic based acute myocardial infarction (AMI) detection device. The AMI detection process uses heat stabilized human serum albumin (HSA) magnetic microspheres and specific antibodies to create a magnetic immunoassay used in the detection of AMI. Microanalysis systems have several advantages over conventional analysis systems due to their sensitivity, reliability and the amount of... Show moreCharacterization of fluid with suspended nanoparticles in microchannels has been studied as a part of a microfluidic based acute myocardial infarction (AMI) detection device. The AMI detection process uses heat stabilized human serum albumin (HSA) magnetic microspheres and specific antibodies to create a magnetic immunoassay used in the detection of AMI. Microanalysis systems have several advantages over conventional analysis systems due to their sensitivity, reliability and the amount of anlaytes needed for the test. The microchannels used in this work were fabricated at Sandia National Laboratories (SNL) using a SwIFTâ¢ microfabrication surface micromaching process. Micro channels made of Poly(dimethylsiloxane)-glass (PDMS-glass) designed and fabricated at the Department of Chemistry at the Florida State University were also used in this work. The SwIFTâ¢ microchannels had dimensions of 6µm in height, 20µm in width and 200µm in length where as the PDMS-glass microchannels had dimensions of 40µm in height, 200µm wide and 13mm in length. Characterization of the microchannels was accomplished using a variety of techniques. The first method used to characterize the microchannels was to used a head pressure-flow set up to determine the pressure and flow characteristics of the SwIFTâ¢ microchannels with the different fluids that the biodiagnostic process calls for, with average mass flow rate being 1.9x10-2 µg/s and Reynolds number of 1.45 at a pressure of 23kPa for a typical channel, these values approach the upper limit of the work accomplished. Since the HSA microspheres, 1µm in diameter and less, play a critical role in the detection protocol their compatibility to the SwIFTâ¢ microchannels was investigated. Results showed the HSA microspheres agglomerated and adsorbed to the walls of the channels. Fluorescence correlation spectroscopy (FCS) was attempted on the SwIFTâ¢ microchannels with 200nm and 40nm beads and the same conclusion of agglomeration and adsorption was reached which made these channels not suitable for adaptation in the microanaylsis system considered for AMI detection. PDMS-glass microchannels head pressure-flow rates were also investigated showing an average mass flow rate of 1.76x10-1µg/s and a Reynolds number of 1.03 at a pressure of 4.5kPa. FCS was preformed on these channels successfully without any signs of agglomeration, though some adsorption of the beads to the walls of the channel was evident. FCS measured max velocity was equal to approximately 6.6 cm/s. Thus it is concluded that microchannels of similar sizes of the PDMS-glass will be needed in the microanalysis system that is being developed to detect for AMI markers. Show less

Date Issued

2004

Identifier

FSU_migr_etd-0470

Format

Thesis

Title

Characterization of Sapphire: for Its Material Properties at High Temperatures.

There are numerous needs for sensing, one of which is in pressure sensing for high temperature application such as combustion related process and embedded in aircraft wings for reusable space vehicles. Currently, silicon based MEMS technology is used for pressure sensing. However, due to material properties the sensors have a limited range of approximately 600°C which is capable of being pushed towards 1000°C with active cooling. This can introduce reliability issues when you add more parts... Show moreThere are numerous needs for sensing, one of which is in pressure sensing for high temperature application such as combustion related process and embedded in aircraft wings for reusable space vehicles. Currently, silicon based MEMS technology is used for pressure sensing. However, due to material properties the sensors have a limited range of approximately 600°C which is capable of being pushed towards 1000°C with active cooling. This can introduce reliability issues when you add more parts and high flow rates to remove large amounts of heat. To overcome this challenge, sapphire is investigated for optical based pressure transducers at temperatures approaching 1400°C. Due to its hardness and chemical inertness, traditional cutting and etching methods used in MEMS technology are not applicable. A method that is being investigated as a possible alternative is laser machining using a picosecond laser. In this research, we study the material property changes that occur from laser machining and quantify the changes with the experimental results obtained by testing sapphire at high-temperature with a standard 4-point bending set-up. Keywords: Sapphire, Bayesian analysis, thermomechanics, alumina Show less

Propagation of laser beams through complex flow field caused by radar system housing has been an important topic for many years dating back to the mid 1960s. Applications for radar systems range from missile defense, directed energy to target designation and tracking. Complications are introduced when laser systems are no longer stationed on the ground, but instead mounted on airplanes traveling at subsonic, transonic and supersonic speeds. Housing systems have been developed with a variety... Show morePropagation of laser beams through complex flow field caused by radar system housing has been an important topic for many years dating back to the mid 1960s. Applications for radar systems range from missile defense, directed energy to target designation and tracking. Complications are introduced when laser systems are no longer stationed on the ground, but instead mounted on airplanes traveling at subsonic, transonic and supersonic speeds. Housing systems have been developed with a variety of different designs with some designs more optimal for decreasing laser aberrations than others. The work presented strives to characterize flow around a hemispherical configuration (D = 10.16 cm) for a turret housing system in the supersonic flow regime. Multiple diagnostic tests were conducted at the Florida Center for Advanced Aero-Propulsion in the Polysonic Wind Tunnel Facility. Shadowgraph visualization, surface oil flow visualization, static pressure and unsteady pressure data characterized the complicated supersonic flow field around a hemisphere. Observations were conducted at Mach 2 while Reynolds number changed, ReD = 1.8 ∗ 106 and ReD = 3.6 ∗ 106. Complex shock system consisting of a lambda shock and detached bow shock were observed upstream of the hemisphere center through shadowgraph images. While a shock-let system was developed between the foot of the lambda shock and the detached bow shock from the unsteady boundary layer shockwave interaction. Surface oil flow visualization accented the development of an axisymmetric horseshoe vortex and the presence of a secondary shock location upstream of the hemisphere. A centerline static pressure distribution quantified the visualization techniques. A stagnation point of 30◦ was observed on the body for both ReD case. While, flow separation occurred at slightly different locations on the hemisphere; flow separated at 103◦ for ReD = 1.8∗106 and 107◦ for the ReD = 3.6 ∗ 106. Location of flow separation is further strengthen by the unsteady pressure data as the energy fluctuations are less on the separation line for the different Re cases. The study found that flow structures for different ReD cases were similar, except for the strength of the different flow features; as the flow feature magnitudes were greater for ReD = 3.6 ∗ 106 case. Also observed from the unsteady pressure measurement data, the wake structure behind the hemisphere were different in nature as the wake structure for the ReD = 1.8 ∗ 106 case was larger than the ReD = 3.6 ∗ 106 case. Planar Particle Image Velocimetry was conducted in the Pilot Wind Tunnel Facility at the Florida Center for Advanced Aero-Propulsion on a dynamically similar flow (M = 2,ReD = 1.8∗106). Planar PIV for different Z/D planes were also measured on a D = 19.05 mm hemisphere, which highlighted the presence of an expansion fan at the apex of the hemisphere with decreasing effects on the external flow field as flow moved further away from the centerline of the hemisphere. The results presented in this work characterized supersonic flow around a hemisphere and has laid the groundwork for the development of active or passive flow control techniques in order to minimize flow structures, which ultimately lead to less aero-optical aberrations. Show less

Date Issued

2017

Identifier

FSU_FALL2017_Carnrike_fsu_0071N_14262

Format

Thesis

Title

Characterization of the Flow-Field for Dual Normally Impinging Axi-Symmetric Jets.

In this study, the flow and acoustic field characteristics of dual high-speed axi-symmetric impinging jets will be examined. Initially, the short takeoff and vertical landing (STOVL) facility was redesigned by adding a second jet to the existing model there by achieving a dual jet configuration. This modified facility was designed to simulate aircraft hover in proximity to the ground. Emphasis is placed on the complex behavior of the jets as the nozzle pressure ratio (NPR) is varied to... Show moreIn this study, the flow and acoustic field characteristics of dual high-speed axi-symmetric impinging jets will be examined. Initially, the short takeoff and vertical landing (STOVL) facility was redesigned by adding a second jet to the existing model there by achieving a dual jet configuration. This modified facility was designed to simulate aircraft hover in proximity to the ground. Emphasis is placed on the complex behavior of the jets as the nozzle pressure ratio (NPR) is varied to produce over-expanded, ideally-expanded and under-expanded jet flows. Two nozzle configurations were chosen to simulate dual impinging jets: 1) two converging nozzles (Mach design, Md = 1.00) and 2) a converging nozzle (Md = 1.00) and a converging-diverging (CD) nozzle (Md = 1.50). The experimental results described in this thesis include shadowgraph flow visualization, surface pressure measurements, and near-field acoustic measurements. Shadowgraph flow visualization was used to observe the acoustic field and the coupling between dual jets for various NPR combinations. Mean surface pressure measurements were obtained for impinging jet configurations which analyzed the jet behavior for ground plane separations ranging from x/D = 2 to 10. These measurements provided information regarding the footprint of the flow-field, particularly the fountain flow behavior. It was found that there is a shift in the fountain flow region which occurs when the NPR of one jet was substantially higher than the supplementary jet. Unsteady pressure measurements and near-field acoustic measurements investigated the presence of a feedback loop that occurs for both free and impinging jets, under certain conditions. The presence of tones, either screech or impingement, was clearly evident from the spectral peaks in the near-field noise spectra. When such tones are present, the corresponding flow-field images show strong acoustic waves. Show less

There has been growing use of microscale flowfields in a diverse range of applications, including active flow control. While these actuators have proven effective, further investigation would increase the understanding of these flowfields from a fundamental fluid mechanics aspect and assist in their optimization. Current flow visualization techniques lack either temporal or spatial resolution necessary to resolve small-scale and high-speed flow structures. Therefore, a laser-based... Show moreThere has been growing use of microscale flowfields in a diverse range of applications, including active flow control. While these actuators have proven effective, further investigation would increase the understanding of these flowfields from a fundamental fluid mechanics aspect and assist in their optimization. Current flow visualization techniques lack either temporal or spatial resolution necessary to resolve small-scale and high-speed flow structures. Therefore, a laser-based microschlieren system has been developed to image several microscale flowfields, including: a 1mm free jet, a small-scale Hartmann tube, several variations of a Resonance-Enhanced Microjet (REM) actuator, and a sparkjet actuator. Laser-induced breakdown in argon is used to generate a light source with a ~10 nanosecond pulse width, which is capable of freezing features present in each of these small-scale, high-speed flows. This light source is coupled with a high-magnification schlieren system with a resolution of 140 pixels/mm to acquire high spatial and temporal resolution schlieren images. Through the use of this technique, various measurements such as shock oscillation displacements, jet front velocities, phase correlations between the aeroacoustic structures, etc. were acquired and compared with acoustic, pressure, and temperature measurements. The results show that the REM actuator has the capability to produce microjets with velocities pulsing from near zero to supersonic, while operating at high frequencies (1-10kHz). Studies from the sparkjet actuator using this new technique found shocks in the exhaust indicating local high-speed flow, which has previously not been seen. Lastly, the instantaneous images captured with the laser-based microschlieren system of the sparkjet actuator and one variation of the REM actuator were compared with snapshots from CFD simulations. Favorable results were found for the simulation of the REM actuator, but the sparkjet actuator simulation requires refinement. This new flow visualization technique has generated exceptional results, and will be a useful tool for researchers in future studies. Show less

Date Issued

2011

Identifier

FSU_migr_etd-4415

Format

Thesis

Title

A Comparison of Pole Assignment & LQR Design Methods for Multivariable Control for Statcom.

Creator

Xing, Liqun, Department of Mechanical Engineering, Florida State University

Abstract/Description

The static synchronous compensator (STATCOM) is increasingly popular in power system application. In general, power factor and stability of the utility system can be improved by STATCOM. Specifically, STATCOM can stabilize a given node voltage and compensate for the power factors of equipment serviced by that node. The dynamic performance of STATCOM is critical to these performance and stability function. STATCOM is a multiple input and multiple output system (MIMO), which can be presented by... Show moreThe static synchronous compensator (STATCOM) is increasingly popular in power system application. In general, power factor and stability of the utility system can be improved by STATCOM. Specifically, STATCOM can stabilize a given node voltage and compensate for the power factors of equipment serviced by that node. The dynamic performance of STATCOM is critical to these performance and stability function. STATCOM is a multiple input and multiple output system (MIMO), which can be presented by a mathematic model. Recently, full MIMO state feedback by pole assignment has been shown to be an improvement over classical PI control. In this thesis, an optimal linear quadratic regulator (LQR) design is a compared to the pole assignment design for transient dynamic performance of STATCOM. It was found that LQR controllers do not offer significant performance improvement to pole assignment. However, as a design method the determination of state feedback gains is easier using the LQR method Show less

Control of Dynamic Stall using microjet perturbation at the upper, leading edge was studied experimentally in a subsonic wind tunnel facility. A NACA 0015 airfoil was fabricated with a field of microjets (200- or 400-micrometers in diameter) to study the effectiveness of control. It was tested in subsonic flow velocities of Mach 0.3 and 0.4 while being dynamically pitched sinusoidal between 0- and 20-degrees at reduced frequencies of 0.05 and 0.10. The Point Diffraction Interferometry (PDI)... Show moreControl of Dynamic Stall using microjet perturbation at the upper, leading edge was studied experimentally in a subsonic wind tunnel facility. A NACA 0015 airfoil was fabricated with a field of microjets (200- or 400-micrometers in diameter) to study the effectiveness of control. It was tested in subsonic flow velocities of Mach 0.3 and 0.4 while being dynamically pitched sinusoidal between 0- and 20-degrees at reduced frequencies of 0.05 and 0.10. The Point Diffraction Interferometry (PDI) technique was utilized to qualitatively visualize the general flowfield and quantitatively to determine the leading edge surface pressure distribution. In addition, a high speed pressure transducer was placed at the 7.5-percent chord location on the upper surface. The airfoil exhibits typical characteristics of dynamic stall until the microjets were activated including boundary layer separation, formation and shedding of a dynamic stall vortex, and a loss in leading-edge suction pressure. However, with microjet control activated the flow over the airfoil appears to remain attached at angles of attack well beyond the static and dynamic stall angles. All data showed no evidence of dynamic stall occurring using this control method up to the maximum angle of attack of 20-degrees. The PDI data shows a slight loss in peak pressure with control, as compared to the uncontrolled case, at low angles of attack. However, the controlled case does not exhibit the large loss in leading-edge suction pressure and does not have a strong hysteresis variation during the cycle, indicating the suppression of dynamic stall. This control method also alleviates shock induced separation in the Mach 0.4 case by preventing shocks from forming at the airfoil's leading edge area. Control was also tested with 200-micrometer diameter microjets with similar results but was slightly less effective even with a higher mass flow rate, making the smaller microjet option less desirable. Show less

Adaptive materials are typically known as materials that convert one form of energy into another. Well-known examples include ferroic materials (ferroelectric, ferromagnetic, shape memory alloys), dielectric elastomer, and azobenzene liquid crystal polymer networks. Many of these materials possess the ability to convert electric/magnetic, thermal, or chemical energy into mechanical energy and vice versa. Whereas these materials have been studied extensively, the underlying multiphysics... Show moreAdaptive materials are typically known as materials that convert one form of energy into another. Well-known examples include ferroic materials (ferroelectric, ferromagnetic, shape memory alloys), dielectric elastomer, and azobenzene liquid crystal polymer networks. Many of these materials possess the ability to convert electric/magnetic, thermal, or chemical energy into mechanical energy and vice versa. Whereas these materials have been studied extensively, the underlying multiphysics coupling and micro- to nano-structure interactions still provide a fertile research area to understand and optimize such materials. This dissertation is focused on the analysis and modeling of specific adaptive materials with particular emphasis on complex electromagnetic interactions and chemical flux in solid materials. We study two kinds of new adaptive materials 1) self-assembling protein nanofibers and 2) photomechanical azobenzene liquid crystal network (azo-LCN) films. The formation and evolution of protein nanofibers are quantified using a new phase field modeling framework and are compared to transmission electron microscopy (TEM) measurements and time-dependent growth measurements given in the literature. Calculations based on the theoretical framework are implemented numerically using a nonlinear finite element phase field modeling approach that couples Allen-Cahn and Cahn-Hilliard equations. These results provide a new modeling tool that couples underlying monomer structure with self-assembling nanofiber behavior. In contrast, the azo-LCN films also have been studied to understand the photochemical coupling on macroscale deformation. The photo-induced strain of azo-LCN films are examined using a large deformation photomechanical shell model to quantify the effect of polarized light interactions with the material. The model comparisons of static deformation illustrate differences in internal photostrain and deformation as a function of composition and external mechanical constraints. Preliminary numerical analysis and comparison with data are presented using the finite element method. This preliminary work has motivated the need for a higher accuracy computational approach to resolve the aforementioned protein self-healing, photo-striction, and more complicated multiphysics conditions. Toward this end, a general field-coupled framework for modeling a broad range of adaptive materials is initiated. The aim is to enhance our fundamental knowledge of the field-coupled microstructure of solid materials. Both electromagnetic field propagation and microstructure evolution are investigated with particular interest in understanding photomechanical behavior of azo-LCNs. Correspondingly, the Maxwell's equations and Allen-Cahn equation are coupled to simulate the evolution of microstructure under the exposure of electromagnetic waves. The interactions between field and microstructure are effectively quantified within the proposed field-coupled system. This numerical framework can be applied to a variety of adaptive materials including azo-LCNs as well as other light coupled materials. To further advance our study of adaptive materials and field-coupled behavior, the Discontinuous Galerkin Spectral Element Method (DGSEM) is applied. The DGSEM is an excellent numerical method for wave propagation, fluid dynamics, and phase evolution problems due to its higher accuracy and treatment of discontinuities. The DGSEM allows for the discontinuity between the element boundaries using what is known as a Riemann flux condition, the high order polynomials of spectral methods provide high accuracy with less computational penalties. These two characteristics are particularly useful in the computation of the microstructure of adaptive materials due to the complex microstructure and electromagnetic waves of light. We apply the DGSEM to solve the reflection and transmission of electromagnetic waves along the interface of dissimilar materials, transduction of azobenzene liquid crystal isomers, and the respective field-coupled characteristics. The numerical solutions shown in this dissertation illustrate the application of DGSEM on complex photomechanically coupled azobenzene liquid crystals. Although the proposed field-coupled theory and associated DGSEM algorithm are applicable to model various adaptive microstructures, we utilize this advanced framework to help understand the trans-cis-trans photoisomerization of azobenzene liquid crystal and its interactions with the electromagnetic fields. The numerical solutions disclose the complicated evolution of photo-responsive liquid crystals and attenuation of optical waves and present transient results on a two-dimensional domain. An auxiliary differential equation method is introduced to model the attenuated light propagating through the linear dispersive liquid crystal. The trans-cis, cis-trans, and trans-cis-trans transduction are simulated using a vector order phase field method and the DGSEM numerical method. Particularly, the thermodynamic path during different photoisomerization processes is studied by comparing the ratio between polarization and the Landau coefficients. In the fully field-coupled implementation for the light and azobenzene liquid crystals, we are able to quantify time-dependent behavior associated with electric fields and liquid crystal orientation, which provide useful information for future materials development and engineering applications. Show less

Solar thermal technology is competitive in some very limited markets. The most common use for solar thermal technology has been for water heating in sunny climates. Another use is for power production, such as the Vanguard system and the Shannendoah Valley Parabolic dish system. However, due to the complex design and costs of production and maintenance, solar thermal systems have fallen behind in the world of alternative energy systems. The concentrated solar thermal energy system constructed... Show moreSolar thermal technology is competitive in some very limited markets. The most common use for solar thermal technology has been for water heating in sunny climates. Another use is for power production, such as the Vanguard system and the Shannendoah Valley Parabolic dish system. However, due to the complex design and costs of production and maintenance, solar thermal systems have fallen behind in the world of alternative energy systems. The concentrated solar thermal energy system constructed for this work follows that of the conventional design of a parabolic concentrator with the receiver placed along the line between the center of the concentrator and the sun. This allows for effective collecting and concentrating of the incoming solar irradiation. The concentrator receives approximately 1.064 kW/m2 of solar insolation (dependent upon time of year), which is concentrated and reflected to the receiver. By concentrating the incoming radiation, the operating temperature of the system is increased significantly, and subsequently increases the efficiency of the conversion from sunlight to electricity. For the current system, with a concentration ratio of 96, the concentrator is theoretically capable of producing temperatures upwards to 712 degrees centigrade. However, due to degradation of the optics and other various factors, temperatures as high as 560 degrees centigrade have been achieved. It was found that the collector (concentrator + receiver) yields an efficiency of 95.6 percent. The system converts this concentrated solar energy to electric energy by use of a Rankine cycle which is operated intermittently; determinant by operating temperature. The efficiency of the Rankine cycle for this system was determined to be 3.2 percent, which is 10.3 percent of its Carnot Efficiency. The system has a solar to electric power conversion of 1.94 percent with a peak electric power production of 220 Watts. The rousing point for this particular system is the simplicity behind the design, with it being simple enough to be maintained by an ordinary bicycle mechanic. This makes the system versatile and ideal for use in off-grid and less tech-savvy areas. This work serves mostly as a proof of concept. Show less

Through limb structure and neuromuscular control, animals have demonstrated the ability to navigate obstacles and uneven terrain using a variety of different mechanisms and behaviors. Learning from the capabilities of animals, it is possible to develop robotic platforms that can aid in the study of these motions towards the production of new technologies for military, search and rescue, and medical applications. To produce these systems, it is important to first understand the underlying... Show moreThrough limb structure and neuromuscular control, animals have demonstrated the ability to navigate obstacles and uneven terrain using a variety of different mechanisms and behaviors. Learning from the capabilities of animals, it is possible to develop robotic platforms that can aid in the study of these motions towards the production of new technologies for military, search and rescue, and medical applications. To produce these systems, it is important to first understand the underlying dynamics and design principles existent in nature that afford creatures such dexterous and agile movements. The creation of robots with legs provide a means for studying different aspects of the dynamics of legged locomotion. This includes investigations of limb coordination for gait controller design, the role of passive compliance in dynamic running, mechanical leg design and configuration for optimal energetic output, and scalability of legged systems in both simulation and through experimentation. This thesis aims to provide insight into the design and implementation of terrestrial robotic platforms with legs. Show less

Supersonic impinging jet flows are dominated by the presence of a feedback loop between the flow and acoustic fields, which leads to many adverse phenomena such as highly unsteady loads on the nearby surfaces, a drastic increase of noise level, and a dramatic lift loss in hover. It has been demonstrated by Alvi et al. (2000, 2003) and Shih et al. (2001) that arrays of microjets near the nozzle exit can be used to disrupt the feedback loop, thus reducing these undesired effects. However, the... Show moreSupersonic impinging jet flows are dominated by the presence of a feedback loop between the flow and acoustic fields, which leads to many adverse phenomena such as highly unsteady loads on the nearby surfaces, a drastic increase of noise level, and a dramatic lift loss in hover. It has been demonstrated by Alvi et al. (2000, 2003) and Shih et al. (2001) that arrays of microjets near the nozzle exit can be used to disrupt the feedback loop, thus reducing these undesired effects. However, the effectiveness of the control was found to be strongly dependent on the ground plane distances and jet operating conditions. Current research was carried out at the same facility used by Alvi et al. (2000, 2003) and Shih et al. (2001). However, this investigation focuses on understanding the physical mechanism behind microjet control, and, as a result, devising optimum control strategies. For this purpose, a comprehensive parametric study was carried out. The test matrix chosen included microjet operating pressure, microjet angle, microjet space, the use of micro-tabs instead of microjets and the spatial distribution of microjets relative to the main jet. Marked improvement in the reduction of flow unsteadiness and related adverse effects was achieved in the current study. Planar and three-dimensional velocity field measurements were made using Particle Image Velocimetry (PIV). The results obtained from these detailed velocity field measurements were found to be consistent with acoustic data and were further examined to explore the physical mechanisms behind microjet control. The velocity/vorticity measurements clearly reveal that the activation of microjets introduces strong streamwise vorticity in the form of well-organized, counter-rotating pairs while concomitantly significantly reducing azimuthal vorticity. Such experimental evidence suggests that the generation of these streamwise vortices is the result of the vorticity tilting and stretching mechanisms initiated when the microjets interact with primary shear layer instabilities. The emergence of these longitudinal structures weakens the large-scale axisymmetric structures in the jet shear layer while also introducing stronger three-dimensionality into the flow. Both these factors lead to a weakening of the feedback loop and accounts for the reduction of flow unsteadiness. These results also show a significant reduction in the near-field turbulent intensities with the activation of microjets, which is consistent with the reduction of the near-field OASPL. Remarkably, all these effects are achieved by using a mass flow rate less than 0.5% of the primary jet mass flux. Show less

Date Issued

2005

Identifier

FSU_migr_etd-1035

Format

Thesis

Title

Control of the Stiffness of Robotic Appendages Using Dielectric Elastomers.

A new robotic leg design is presented that utilizes dielectric elastomers (3M VHB 4910) to rapidly control stiffness changes for enhanced mobility and agility of a field demonstrated hexapod robot. It has been shown that stiffness changes of electro-active membranes made of dielectric elastomers can overcome challenges with other polymer materials that use heat to create modulus and stiffness changes. Applied electric fields eliminate issues with thermal transport rates and thermo-mechanical... Show moreA new robotic leg design is presented that utilizes dielectric elastomers (3M VHB 4910) to rapidly control stiffness changes for enhanced mobility and agility of a field demonstrated hexapod robot. It has been shown that stiffness changes of electro-active membranes made of dielectric elastomers can overcome challenges with other polymer materials that use heat to create modulus and stiffness changes. Applied electric fields eliminate issues with thermal transport rates and thermo-mechanical delaminatation. The dielectric elastomer is characterized uniaxially to understand its hyperelastic and viscoelastic properties. The uniaxial data is fit to a hyperelastic and viscoelastic finite deformation model. The material is then pre-stretched biaxially to stretch ratios ranging from 200%, 300% and 400%. A set of electro-mechanical transverse load experiments are then utilized to obtain up to 92% reduction in stiffness that is controlled by an electric field. The results are compared to a finite deformation membrane finite element model to understand and improve field driven stiffness changes for real-time robotic applications. Show less

Date Issued

2012

Identifier

FSU_migr_etd-5055

Format

Thesis

Title

Cooling Concept for the Armature Winding of High Temperature Superconducting Motor.

The present study reports a numerical heat transfer approach, an effort devoted to defining a cooling concept for a high performance synchronous motor that has a High Temperature Superconductor (HTS) field winding. A lumped-circuit approach and a numerical, FEM analysis of a 500 kW HTS motor with an axial cooling channel is demonstrated in the report presented here. The thermal analysis performed using equivalent, lumped thermal network shows a simplified circuit which is aimed at delivering... Show moreThe present study reports a numerical heat transfer approach, an effort devoted to defining a cooling concept for a high performance synchronous motor that has a High Temperature Superconductor (HTS) field winding. A lumped-circuit approach and a numerical, FEM analysis of a 500 kW HTS motor with an axial cooling channel is demonstrated in the report presented here. The thermal analysis performed using equivalent, lumped thermal network shows a simplified circuit which is aimed at delivering fast, design class results that can be solved analytically and also more complex schemes which are aimed at assessing variable regimes are solved numerically by a circuit simulator (QUCS). Both approaches are valuable, and complement each other in the quest for a meaningful preliminary design. There are several difficulties related to standard lumped thermal circuit models such as concentrated heat sources, lack of detailed thermal load information, etc., and all these drawbacks can be overcome by a more detailed convection and conduction heat transfer model which are conveniently solved by numerical analysis, e.g. by FEM technique using FLUENT package. Various models that were implemented using the FEM technique include different coolants and a fin model. The coolants that were used in the present study are air and water. The maximum temperature attained in the stator for air and water is 382 K and 345 K respectively for limiting Reynolds number for laminar flow. Another approach to cool the motor is by attaching a fin of copper material in the cooling channel. This fin can be used as an alternative for water as it also bring down the maximum temperature in the motor to 350 K. Show less

Great interest has been shown for the development of an All Electric Aircraft. There are many possible benefits and applications for the development of an All Electric Aircraft, such as monitoring severe weather or exploring the surface of other planets, and ultimately in civil aviation, a zero-emission aircraft. Design of the size and weight of the electrical systems for airplane use is important and a critical factor in this development is the propulsion of the aero-vehicle. One method to... Show moreGreat interest has been shown for the development of an All Electric Aircraft. There are many possible benefits and applications for the development of an All Electric Aircraft, such as monitoring severe weather or exploring the surface of other planets, and ultimately in civil aviation, a zero-emission aircraft. Design of the size and weight of the electrical systems for airplane use is important and a critical factor in this development is the propulsion of the aero-vehicle. One method to increase power density of a motor is to use superconducting components. The development of a superconducting motor that provides enough power for an airplane is discussed. A Cessna-type aircraft is to be powered by a motor that utilizes high temperature superconducting (HTS) components in the inductor. This motor is a novel design that uses both BSCCO (bismuth strontium calcium copper oxide) tape wound in pancake shapes and single domain, bulk YBCO (yttrium barium copper oxide) plates to create powerful magnetic fields capable of meeting requirements for an aircraft. The HTS inductor design generates a magnetic field outward to a rotating, non-superconducting armature. The BSSCO pancakes generate a magnetic field to trap magnetic flux in the YBCO plates via the Field Cooling method (FC). The use of FC creates very powerful magnetic fields but requires a multi-step cooling schedule for the inductor design. To properly trap flux using FC, the BSCCO pancakes must first be cooled to the operating temperature and generate an applied magnetic field while the bulk YBCO plates remain above the critical temperature. The YBCO plates are then cooled near the operating temperature, thus trapping flux in the plates. The current in the pancakes is then reversed and the magnetic fields are generated, then the YBCO plates are further cooled to the steady state temperature. This process of cooling the BSCCO pancakes and then cooling the YBCO plates is called the 3-stage cooling. The cooling of the motor is by conduction due to the mobile application of aero-propulsion. The conduction-cooled inductor is constructed along with a cooling apparatus that includes an aluminum central cylinder attached to a cryocooler, G10 rings, and heaters that aid in the 3-stage cooling process. Simulations were performed that model the heat loads, cooling schedule from room temperature to operational temperature, and the 3-stage cooling to aid in the design. These modeling results show the temperature gradients in the inductor and HTS components and are verified experimentally. A full-scale, mockup inductor has been constructed and is cooled with a cryocooler in a cryostat. The cooling inductor final design is shown with modeling results and the proof-of-principle or a motor utilizing HTS materials in the inductor has been provided. A prototype of the motor should be built and tested based on these electromagnetic and cooling designs. The use of heaters near the YBCO plates is required in the 3-stage cooling design. The YBCO has trapped-flux that is dependent on the operating temperature and the stability of the trapped-flux is critical to the motor design. Work has been done that experimentally tests the stability of trapped flux in YBCO plates. A heat impulse is inputted into a YBCO sample that is fully penetrated in current via FC. The experiments were performed in a sample chamber that has temperature and applied magnetic field controllability. The change in the magnetic field and temperature of the sample is measured and analyzed before and after the heat pulse using Hall probes. The experimental data suggests that there is no thermal runaway loss in the trapped-magnetic flux for a small heat input and an operating temperature for which the sample has maximum stability. To explain the physics of the trends exhibited in the data, two models were developed. The first model uses an analytical approach to capture the overall trends exhibited by the data. The analytical model uses an energy balance based on the stored magnetic energy loss and change in thermal energy before and after the heat pulse is input into the sample. The second model is a finite element analysis approach using commercial software (Comsol) to gain a more in-depth analysis of the internal changes in the sample during the heat pulse. The Comsol model provides a tool to study the effect of the heat pulse on the current density and the effect of the cooling environment surrounding the sample. The models are able to capture the trends suggested by the experiment and provide insight into the fundamental phenomena that happen during the heat pulse. The sample studied in the experiment does indeed have a maximum stability point and it is explained by the modeling work. A cooling apparatus was designed to cool the inductor of a HTS motor. The electro-magnetic design utilizes field cooling to trap flux and this was accomplished with a 3-stage cooling process. The cooling design was validated using simulations and experimental data. The cooling apparatus showed the feasibility of the inductor to trap flux in the plates. The stability of the trapped flux was also studied. Experimental data shows that there is no thermal runaway when heat is inputted into a sample and an operating temperature exists that suggests a maximum stability. The physics of the stability experiment was uncovered using an analytical model and a FEA model. Also shown was the effect of the cooling environment on the sample during the heat impulse. The stability models showed that the data are the results of the cooling environment and the competing effects of current density and specific heat, both functions of temperature. Show less

Date Issued

2009

Identifier

FSU_migr_etd-0821

Format

Thesis

Title

Coordination of Multiple Active Front End Converters for Power Quality Improvement.

The proliferation of semiconductor-based nonlinear devices in modern power systems has caused serious concern over the power quality problems. This dissertation proposes a control strategy to coordinate multiple active front-end converters so that harmonic currents as well as reactive power generated by the nonlinear load can be compensated. The objective of the proposed coordination strategy is to fully utilize the potential of the existing active front-end converters and minimize the space... Show moreThe proliferation of semiconductor-based nonlinear devices in modern power systems has caused serious concern over the power quality problems. This dissertation proposes a control strategy to coordinate multiple active front-end converters so that harmonic currents as well as reactive power generated by the nonlinear load can be compensated. The objective of the proposed coordination strategy is to fully utilize the potential of the existing active front-end converters and minimize the space as well as the cost requirement for the power system where power quality improvement is needed. Under the proposed coordination strategy, the power quality distortion caused by a large nonlinear load is measured by a central controller and the corresponding power quality compensation task is distributed to multiple active front-end converters. The percentage of power quality compensation task assigned to an individual active converter is determined proportionally to its instantaneous power margin. The proposed coordination strategy can be a fairly flexible and economical solution for power quality improvement especially for the places where multiple active front-end converters are required and/or space-limited systems, such as manufacturing factories and/or shipboard or aircraft power systems. Both non-real-time and real-time simulation results show that the proposed coordination strategy has good performance and is both effective and promising. Show less

This dissertation presents a study of steady He II (superfluid helium) counter flow heat transfer in porous media. Porous insulation were suggested as potential alternatives to conventional fully impregnated insulations in superconducting magnet technology. Superconducting magnets are usually cooled with He II. Use of porous insulation requires thus a good knowledge of the behavior of He II within porous materials, when set in motion or exposed to a heat source. The present work was focused... Show moreThis dissertation presents a study of steady He II (superfluid helium) counter flow heat transfer in porous media. Porous insulation were suggested as potential alternatives to conventional fully impregnated insulations in superconducting magnet technology. Superconducting magnets are usually cooled with He II. Use of porous insulation requires thus a good knowledge of the behavior of He II within porous materials, when set in motion or exposed to a heat source. The present work was focused on the design of an apparatus capable of performing both steady and transient counterflow measurements in He II saturating a porous material with a geometry similar to potential candidate porous insulations. Those will most likely be composed of tapes of pre-impregnated woven ceramic fibers, forming a highly anisotropic compound, with a wide pore size distribution. The samples were provided by Composite Technology Development Inc. and are circular pellets (3.08 mm thick and 28.58 mm in diameter) of 20 compressed layers of pre-impregnated woven magnet insulation. The porous material was carefully characterized prior to experimental runs in He II. The samples exhibit a porosity and a permeability of respectively 20+-1% and 0.95x10^-14 m^2 for water measurements. The woven fiber rovings, composing the insulation, were found to be 0.04 mm^2 of average cross sectional area with fibers of average diameter of 10.6 micron. The He II experimental apparatus is composed of a vacuum insulated open channel whose top extremity is closed to a Minco heater. The temperature differences and pressure drops across the porous plug were measured by two Lakeshore barechip Cernox 1050BC thermometers and a Validyne DP10-20 differential pressure sensor. Applied heat fluxes ranged up to 0.5 kW/m^2 of sample cross section. Steady temperature differences, up to 570 mK, and pressure drops, up to 1800 Pa (limit of the sensor), measurements were performed at bath temperatures ranging from 1.6 to 2.1 K. In the low heat flux regime, the permeability data corroborate room temperature measurements. In the high heat flux regime however, we show evidence of the failure of previous models based on the inclusion of the tortuosity in the turbulent equation. We propose to include a constriction factor denoting an average maximum change in cross section in the heat path in addition to the increased path length denoted by the tortuosity. In the turbulent regime, this constriction factor is predominant as it enters in the model with a cubic power. Measurements of the critical characteristics, corresponding to the point of transition from the laminar regime, where Darcy law is applicable to the non-linear regime, where the heat flux adopts its characteristic cubic relationship, corresponding to the appearance of turbulence within He II are also reported. We obtained critical heat fluxes ranging from 20 to 70 W/m^2, Reynolds numbers of 0.5 to 4 and normal fluid velocities from 0.5 to 2.5 mm/s, varying with bath temperature. To confirm the room temperature measurements of permeability, we also conducted a forced flow experiment. Unfortunately, the flow range covered is outside of the laminar regime and does not permit an accurate estimation of the permeability. The results are however favorably comparable to earlier data recorded in the turbulent regime in similar flow conditions but with very different materials. Show less

Date Issued

2010

Identifier

FSU_migr_etd-0855

Format

Thesis

Title

Cryogenic Cooling System by Natural Convection of Subcooled Liquid Nitrogen for HTS Transformers.

A new concept of thermal design to optimize the operating temperature of HTS magnets is developed, aiming simultaneously for compactness and efficiency. The optimization procedure seeks the operating temperature to minimize the power consumption in steady state. This procedure includes the modeling of the critical properties of HTS conductors, the dimensions of HTS windings, the heat transfer analysis for cooling load estimate, the thermal interface between the HTS windings and cryocooler,... Show moreA new concept of thermal design to optimize the operating temperature of HTS magnets is developed, aiming simultaneously for compactness and efficiency. The optimization procedure seeks the operating temperature to minimize the power consumption in steady state. This procedure includes the modeling of the critical properties of HTS conductors, the dimensions of HTS windings, the heat transfer analysis for cooling load estimate, the thermal interface between the HTS windings and cryocooler, and the thermodynamic evaluation of the required refrigeration. Finally, this method is applied to two specific cooling systems for HTS transformers: a liquid-cooled system with pancake windings and a conduction-cooled system with solenoid windings. The optimum temperature turns out to be slightly above 77 K, the normal boiling temperature of nitrogen, for both the liquid-cooled system and the conduction-cooled system, but could vary considerably by the magnitude of AC loss in the HTS conductors. Operation at a temperature below 77 K can be justified, if the amount of AC loss is substantially reduced or the savings in capital investment by the compactness is significant in comparison with the operational cost. A new cryogenic design for cooling HTS transformers, the so called natural convection system, is proposed in accordance with the results of an optimization study and the considerations of liquid nitrogen as cooling media. In the natural convection system, HTS windings are immersed in a liquid nitrogen bath where the liquid is cooled simply by copper sheets vertically extended from the coldhead of a GM cryocooler above the windings. Liquid nitrogen in the gap between the windings and the copper sheets develops a circulating flow by the buoyancy force in the subcooled state. A comprehensive heat transfer analysis is performed to evaluate the proposed cooling system. The heat transfer coefficient for natural convection is predicted from the existing engineering correlations in which the temperatures of two surfaces are uniform, and then the axial temperature distributions of HTS windings, copper sheets, and liquid-vessel wall are calculated analytically and numerically, taking into account the distributed AC loss and the thermal radiation on the walls. The warm-end of the HTS windings is maintained at only 2~3 K above the freezing temperature of nitrogen (63 K) at atmospheric pressure with acceptable values for the height of HTS windings and the thickness of copper sheets. Such a system based on cooling by natural convection with subcooled liquid nitrogen could be an excellent option for HTS transformers, when considering all aspects of compactness, efficiency, and reliability. In order to confirm the feasibility of the new design for cooling HTS transformers, a natural convection cooling experiment was designed and constructed. The primary purpose of the experiment, therefore, is to simulate the thermal environment as closely as possible to the proposed cooling system. The experimental apparatus is approximately 1:5 scale and has the same configuration as the cooling system for Korean HTS transformer, except that an electrical heater is used for simulate the AC loss and the vertical cavity between parallel plates replicates the narrow annular gap between HTS windings and the vertical copper sheets in the cooling system for an HTS transformer. A liquid nitrogen bath is cooled down to nearly the freezing temperature at atmospheric pressure by a vertical copper heat transfer plate thermally anchored to the coldhead of a single-stage GM cryocooler. A parallel copper plate generating a uniform heat flux is placed at a distance so that liquid between the two plates may develop a circulating flow by natural convection. The cold surfaces are continuously maintained below 66 K in subcooled liquid nitrogen for heat fluxes up to 100 W/m2. The vertical temperature distribution on both surfaces is measured in steady state, from which the heat transfer coefficient is calculated and compared with the existing correlations for a rectangular cavity where each vertical surface has a uniform temperature. When the heat flux is smaller than 40 W/m2 or the corresponding Rayleigh number is smaller than 1.6 x 10^8, good agreement is observed between the experiment and correlation because the plate temperatures are relatively uniform in the vertical direction. As the heat flux increases over 40 W/m2 or Rayleigh number exceeds 1.6 x 10^8, however, the heat transfer coefficients are approximately 20~30 % greater than the existing correlations. The thermal boundary conditions in the present experiment with surface temperature decreasing upwards may cause vertically segregated cellular flows in the cavity. These multi-cellular flow patterns can lead to the augmentation of wall-to-wall heat transfer by reducing the effective height of the cavity. Show less

Date Issued

2004

Identifier

FSU_migr_etd-3784

Format

Thesis

Title

Deformation Mechanisms at Atomic Scale: Role of Defects in Thermomechanical Behavior of Materials.

The primary focus of the thesis is to understand the role of defects and interfaces in the deformation of nanoscale structures and systems. Various nanoscale systems such as symmetric tilt-grain boundaries (STGB) in aluminum, topological defects in carbon nanotubes (CNT), hybridization defects in carbon nanotubes and nanoscale interfaces in CNT based composites are investigated using molecular dynamics and statics. In order to further explore the effect of nanoscale interfaces on the... Show moreThe primary focus of the thesis is to understand the role of defects and interfaces in the deformation of nanoscale structures and systems. Various nanoscale systems such as symmetric tilt-grain boundaries (STGB) in aluminum, topological defects in carbon nanotubes (CNT), hybridization defects in carbon nanotubes and nanoscale interfaces in CNT based composites are investigated using molecular dynamics and statics. In order to further explore the effect of nanoscale interfaces on the macroscopic behavior of CNT based composites a multiscale model, which hierarchically employs molecular dynamics and the finite element method is developed. Carbon nanotubes are cylindrical structures of carbon wrapped from a planar hexagonal mesh of atoms. Topological defects are planar irregularities in this hexagonal mesh, while hybridization defects are formed when changes in bonding cause out of plane disturbance. The deformation characteristics of CNTs in presence of both these types of defects are modeled using Brenner's potential. The other material systems studied in this work are symmetric interfaces in aluminum. Symmetric tilt-grain boundaries are a type of grain boundaries with restricted degrees of freedom due to symmetry. The sliding behavior, energetics and effect of magnesium doping in these grain boundaries is investigated using embedded atom method (EAM) potentials in the molecular dynamics setting. Study of deformation has been traditionally under the purview of continuum mechanics; concepts such as stiffness, strength, damage, and fracture are best studied using continuum stress and strain measures. Because of the discrete nature of atoms, these concepts are not clearly understood in atomistic simulations. In this work, different stress measures are employed for Brenner's potential and the criterion for applicability in various conditions is examined. A new methodology to evaluate strains for nanotubes is developed. Local and global deformation characteristics in elastic and inelastic regimes in nanotubes with defects are examined and compared with defect-free nanotubes. It is found that there is a decrease in stiffness of nanotubes in presence of topological defects. The local elastic moduli are found to reduce to 60 % of that of defect-free nanotube. A simple model is developed to predict the reduction in stiffness in presence of a number of defects. In the case of hybridization defects caused by attachment of hydrocarbon functional groups, the elastic modulus is found to improve marginally. In addition, the onset of inelasticity and fracture occur at lower strains in functionalized nanotubes. Interfaces in composites affect the key mechanical properties such as stiffness, strength and fracture toughness. In this work, interfaces in nanotube based composites are modeled as hydrocarbon chemical attachments between the matrix and CNT. Molecular dynamics simulations of fiber pullout tests are then employed to understand the load transfer behavior and quantitatively determine the interface strength. These results are used to generate traction-displacement constitutive relation for a continuum description of interfaces in terms of cohesive zone model. A multiscale methodology is formulated using the atomically informed cohesive zone model to represent interfaces in a finite element formulation. Application of this approach is demonstrated by examining the effect of interface strength on the stiffness of nanotube based composites. Show less

This work focuses on the steps taken to characterize three of the mechanical micropumps developed by the Biomagnetic Engineering Laboratory at Florida State University. This study illustrates the steps taken to bring fluid to the microdevice, corrections of original design failures, computational analysis of the fluid flow in the pumps, development of performance equations and experimental studies to demonstrate the pressure-flow rate curve for one of the three pumps. The entire research... Show moreThis work focuses on the steps taken to characterize three of the mechanical micropumps developed by the Biomagnetic Engineering Laboratory at Florida State University. This study illustrates the steps taken to bring fluid to the microdevice, corrections of original design failures, computational analysis of the fluid flow in the pumps, development of performance equations and experimental studies to demonstrate the pressure-flow rate curve for one of the three pumps. The entire research serves as a foundation for the characterization of three micropumps, the spiral pump, the crescent pump and the Von Karman pump. Methods were developed to both plumb, prime, and isolate the system for pumping. The first task was to correct flaws in the original design for the pumps. Many deficiencies were present that required redesigns. The redesigns varied from the strengthening of cantilever members to the introduction of new gear transmissions. The new designs introduced in this study overcome the shortcomings in the original design. The research performed on the spiral pump focuses primarily on a computational study. The analysis is used to support the work that previously determined performance equations for the device. The study also offers support for several key assumptions that were used to reach these performance equations. The spiral pump was then subjected to internal resistance tests that were used validate the computational study. Computational studies were also performed on the Von Karman pump. This analysis led to expected output flow rates for the device. The study also justified the concept of naming the pump after the classical flow of the Von Karman pump and used this justification for the formulation of a scaled performance equation for the system. Finally, the crescent pump was characterized experimentally. Output flow rates were then measured, thus providing evidence on the viability of the operation of these devices. A performance equation for the system was also developed which predicts the output flow rate of the pump to within 6%. Show less

Date Issued

2004

Identifier

FSU_migr_etd-4129

Format

Thesis

Title

Design and Characterization of a Dielectric Elastomer Based Variable Stiffness Mechanism for Implementation onto a Dynamic Running Robot.

Biological systems show a reliance upon their capability to adapt limb stiffness as a means to achieve dynamically similar locomotion over a wide range of terrains. The versatility of robotic platforms falls short in comparison to their biological counterparts. One possible method to enhance the performance of these systems is to integrate a variable stiffness mechanism into the locomotive structure to aid in their adaptability. To date, many variable stiffness mechanisms have been designed,... Show moreBiological systems show a reliance upon their capability to adapt limb stiffness as a means to achieve dynamically similar locomotion over a wide range of terrains. The versatility of robotic platforms falls short in comparison to their biological counterparts. One possible method to enhance the performance of these systems is to integrate a variable stiffness mechanism into the locomotive structure to aid in their adaptability. To date, many variable stiffness mechanisms have been designed, but they have multiple drawbacks. The current mechanisms are typically too slow to achieve rapid adaptations during dynamic locomotion or too large for implementation onto smaller platforms. It is desirable to have a variable stiffness mechanism that is able to achieve a large reduction in stiffness in the minimal amount of time. This work focuses on the development process of a dielectric elastomer based variable stiffness mechanism as a replacement for traditional springs on a legged hexapedal robot. A simulation is developed assessing the stability benefits of an ideal variable stiffness mechanism actuated over the period of a single stride during dynamic locomotion. The design process is detailed and the characterization of the mechanism in terms of its magnitude for stiffness reduction, transient response to stimuli, and implementability is presented. The newly developed system shows up to an order of magnitude reduction in stiffness at an actuation frequency approximated at 10 Hz. The system is implemented onto an adapted version of the dynamic running robot, iSprawl, and its performance is characterized with respect to forward velocity. Reliability issues in the current manufacturing process pose a potential problem, but new methods are proposed to increase durability and repeatability of the mechanism. Finally, the next generation design for implementation onto a new platform is presented. Show less

This study focuses on characterizing meso scaled pumps. These pumps match in design to micro mechanical pumps produced using surface micromachining technology. The objective of this study is to characterize the performance of the meso scaled pumps experimentally, analytically, and numerically in order to gain a better understanding of the functional behavior of micropumps. Both types of actuations, magnetically and mechanically driven pumps, are considered in this thesis. In the magnetic... Show moreThis study focuses on characterizing meso scaled pumps. These pumps match in design to micro mechanical pumps produced using surface micromachining technology. The objective of this study is to characterize the performance of the meso scaled pumps experimentally, analytically, and numerically in order to gain a better understanding of the functional behavior of micropumps. Both types of actuations, magnetically and mechanically driven pumps, are considered in this thesis. In the magnetic actuation, noninvasive coupling occurs between applied magnetic field and magnetically actuated material deposited on a movable actuator on the pump. Several advantages are reported when utilizing the magnetic actuation, including a reduction in the heat conduction from the motor to the bio fluids and a reduction on the hardware, particularly when using micro systems. A coupler was designed and manufactured to transmit the torque from the motor's shaft to the pump's shaft during mechanical coupling. The three micropumps to be characterized are the spiral pump, Von Karman pump, and crescent pump. These three micro pumps were fabricated at Sandia National Laboratory. In this study, three meso scaled pumps are characterized. The characterization for each mesopump was performed by pumping liquid water. A numerical simulation using CFDRC computer code was also performed for two viscous drag pumps (spiral, and Von Karman), and a comparison between the numerical, and experimental results was performed. Furthermore experimental data was compared to that predicted by analytical solution for spiral and crescent mesopumps. Characterization curves for each mesopump are then produced to provide a description of each pump's performance; moreover factors affecting the pump's performance are discussed. Show less

A haptic interface is a device that accepts as input the motion or force of a human operator, and outputs force or motion to the operator based on a computer simulated (virtual) environment. This thesis describes the design and construction of a one D.O.F haptic interface. The purpose of the interface would be to study virtual reality simulations, time delay in telerobotics communication, and virtual surface stability. Three designswere considered to determine the best choice. The design... Show moreA haptic interface is a device that accepts as input the motion or force of a human operator, and outputs force or motion to the operator based on a computer simulated (virtual) environment. This thesis describes the design and construction of a one D.O.F haptic interface. The purpose of the interface would be to study virtual reality simulations, time delay in telerobotics communication, and virtual surface stability. Three designswere considered to determine the best choice. The design criteria included specificationssuch as low system inertia, imperceptible backlash, high dynamic range, and user comfort. The detailed parts drawings of the design selected were completed using the Solidworks Computer Aided Drawing (CAD) package. The parts were machined and assembled in-house and virtual environments were developed to test the effectiveness of the haptic Show less

The Multiple Parabolic Reflector Flat Panel Collector (MPFC) was designed to heat a working fluid to a temperature of 150oC using the sun. The use of stationary reflectors and a moving receiver tube allow for maximum energy collection with minimum amount of solar tracking. The reflector-receiver combination is placed within an enclosure with multiple reflectors; the top of the enclosure allows solar radiation while stifling thermal losses from convection and radiation to the environment. A... Show moreThe Multiple Parabolic Reflector Flat Panel Collector (MPFC) was designed to heat a working fluid to a temperature of 150oC using the sun. The use of stationary reflectors and a moving receiver tube allow for maximum energy collection with minimum amount of solar tracking. The reflector-receiver combination is placed within an enclosure with multiple reflectors; the top of the enclosure allows solar radiation while stifling thermal losses from convection and radiation to the environment. A concentration ratio of 6 is used with respect to the aperture area of the reflector compared to the surface are of the receiver. The MPFC is a panel collector where the enclosure remains stationary and the receiver moves to track the sun. This is accomplished by combining aspects of flat panel (FP) collectors, compound parabolic concentrators (CPC), and parabolic trough collectors (PTC). The design is based on an analysis performed using ray tracing techniques to estimate the amount of radiation reaching the receiver. It was shown that the amount of possible energy collection is comparable to that of FP and CPC collectors. Computation Fluid Dynamics (CFD) was used to estimate convective heat transfer within the enclosure. Combining the ray tracing and CFD results with a thermodynamic model of the panel, the total performance of the MPFC can be estimated. Experiments were also performed to verify the method of the numerical model, the optical efficiency found from the ray tracing model, and the heat loss found from the CFD solution. It was found that the numerical model solves the system of equations appropriately, the ray tracing is an accurate description to the reflection of the radiation, and the CFD modeled the natural convection within a cavity with appropriate accuracy while remaining a conservative estimation. The final MPFC design is a compilation of the individual studies in a way that is simple while accomplishing its goals. Show less

Date Issued

2013

Identifier

FSU_migr_etd-7959

Format

Thesis

Title

Design and Implementation of a Limit Cycle Negotiation Strategy for Robot Navigation.

Limit cycles can occur when navigating unmanned ground vehicles (UGVs) using behavior-based or other reactive algorithms. Limit cycles occur when the robot is navigating towards the goal but enters an enclosure that has its opening in a direction opposite to the goal. The robot then becomes effectively trapped in the enclosure. This thesis presents a solution to the limit cycle problem for robot navigation in very cluttered environments, for example dense forests. These type of environments... Show moreLimit cycles can occur when navigating unmanned ground vehicles (UGVs) using behavior-based or other reactive algorithms. Limit cycles occur when the robot is navigating towards the goal but enters an enclosure that has its opening in a direction opposite to the goal. The robot then becomes effectively trapped in the enclosure. This thesis presents a solution to the limit cycle problem for robot navigation in very cluttered environments, for example dense forests. These type of environments offer a challenge due to the diversity of shapes and sizes of deadlocks that are likely to appear. A simple deliberative algorithm for detecting and retracting from limit cycles is described. The algorithm uses spatial memory to detect the limit cycle. Once the limit cycle has been detected, a labeling operator is applied to a local map so that the obstacles that form the boundary of the deadlock enclosure are identified. Subsequently, the robot is directed outside the enclosure using a behavior based control system. Once it exits this region, the deadlocked area is designated as off-limits by means of a virtual wall. Finally, the robotic vehicle proceeds to its original target avoiding the virtual wall and the different obstacles that are found on its way. Simulation and experimental results demonstrate the effectiveness of the proposed method. Show less

Date Issued

2006

Identifier

FSU_migr_etd-2341

Format

Thesis

Title

Design of a Biologically Inspired Jumping Mechanism for a Dynamic Running Platform.

Creator

Carbiener, Charles, Department of Mechanical Engineering

Abstract/Description

Many animals are capable of jumping from a running gait. This allows them to quickly overcome a large range of obstacles. A robotic platform capable of running jumps will benefit similarly, and see a great enhancement to its mobility. This thesis presents the design, simulation and preliminary validation of a robotic leg capable of both running and jumping. Two reduced order running models are introduced to investigate the dynamics of running and jumping. These models are used to demonstrate... Show moreMany animals are capable of jumping from a running gait. This allows them to quickly overcome a large range of obstacles. A robotic platform capable of running jumps will benefit similarly, and see a great enhancement to its mobility. This thesis presents the design, simulation and preliminary validation of a robotic leg capable of both running and jumping. Two reduced order running models are introduced to investigate the dynamics of running and jumping. These models are used to demonstrate that a platform can control its trajectory by changing the timing of its jump and to guide the design of a functional prototype. This prototype functions by storing energy by deforming a compliant element, which can then be released into a jump when needed. The prototype was built and several proof of concept tests were performed to show the capabilities of this prototype. Show less

Cobots are specially designed robots that use continuously variable transmissions (CVTs) instead of traditional motor driven joints. Cobots are an attractive choice for telerobotic master controllers because they are safe in contact with humans and are able to produce stable, high quality virtual surfaces that can constrain the motion of the master to directions suitable for telerobotic task completion. This thesis describes the design of a 3-DOF, cable driven, wearable arm master controller... Show moreCobots are specially designed robots that use continuously variable transmissions (CVTs) instead of traditional motor driven joints. Cobots are an attractive choice for telerobotic master controllers because they are safe in contact with humans and are able to produce stable, high quality virtual surfaces that can constrain the motion of the master to directions suitable for telerobotic task completion. This thesis describes the design of a 3-DOF, cable driven, wearable arm master controller and provides the details on the construction and assembly of the shoulder joint. Solidworks CAD was used to design the wearable cobot. After shoulder capstans and shafts were machined the device was assembled and tested. The rotational stiffness for the shoulder joint was found to be 1.58*105 lb-in/rad and the start torque was found to be 16.5 lb-in. Improvements and future work are also discussed. Show less

The design of a unique liquid nitrogen pumping station requires a unique pressure relief valve. This new relief valve must operate at low pressure differentials, work effectively at low cryogenic temperatures, and release a wide range of nitrogen vapor mass flow rates. A floating valve design was selected, one that requires no springs and relieves pressure based upon the weight of the actuating piston. Before testing began, an analytical flow model of pressure loss through the valve was... Show moreThe design of a unique liquid nitrogen pumping station requires a unique pressure relief valve. This new relief valve must operate at low pressure differentials, work effectively at low cryogenic temperatures, and release a wide range of nitrogen vapor mass flow rates. A floating valve design was selected, one that requires no springs and relieves pressure based upon the weight of the actuating piston. Before testing began, an analytical flow model of pressure loss through the valve was completed and valve set pressures were calculated. The purpose of the valve testing was to both prove the concept of the valve and verify results from the modeling. Experimental results revealed accurate agreement between the model and the test for low mass flow rates. However, at high mass flow rates, the model and test results did not agree, as the effects of vortices above the valve were not included within the model. While the basic concept and operation of the floating valve were established, further and more precise testing are required to develop a complete understanding of the valve's operation. Show less

Date Issued

2004

Identifier

FSU_migr_etd-4255

Format

Thesis

Title

Design, Modeling, Construction, and Flow Splitting Optimization of a Micro Combined Heating, Cooling, and Power System.

Combined heating, cooling, and power systems (CHCP) have the ability to provide simultaneous electricity, heating, and cooling at a lower fuel and emissions cost than conventional methods. This technology achieves this by recovering otherwise wasted thermal energy from the exhaust of the prime mover. This work aims to examine the optimal flow splitting of this exhaust stream in a CHCP system between the water heating and refrigeration units. A thermodynamic model was created and an... Show moreCombined heating, cooling, and power systems (CHCP) have the ability to provide simultaneous electricity, heating, and cooling at a lower fuel and emissions cost than conventional methods. This technology achieves this by recovering otherwise wasted thermal energy from the exhaust of the prime mover. This work aims to examine the optimal flow splitting of this exhaust stream in a CHCP system between the water heating and refrigeration units. A thermodynamic model was created and an experimental system was designed, built, and tested. Results from the simulated model show that thermodynamic losses can be minimized in the CHCP system with the proper selection of a splitting fraction. Under this condition maximum first law system efficiency can be achieved. An exergetic analysis confirms the existence of an optimal splitting. An experimental micro CHCP system was built with a bypass valve system that permitted manual control of the exhaust gas splitting fraction. Splitting fractions of X = 0, 0.12, 0.18, 0.45, and 0.9974 could be achieved with this bypass system. Test runs of the system showed that 64%, 83%, and 86% of the thermal energy contained within the hot exhaust gas stream could be recovered under splitting fractions of X = 0.45, 0.18, and 0.12 respectively. First and second law analysis proved that overall system efficiencies of the CHCP system could be significantly improved when compared to system efficiencies of electrical power generation alone. Experimental results were then used to recalibrate the model to better simulate the performance of the experimental CHCP system built for this work. Show less

M, Naveen Prakash, Department of Mechanical Engineering, Florida State University

Abstract/Description

The Coefficient of Thermal Expansion (CTE) of Carbon nanotubes (CNTs) is determined using Molecular Dynamics (MD) simulations. Accurately evaluating CTE using experimental methods still suffers from size restrictions and measurement limitations. Thus, computational methods (MD simulations) prove to be an ideal tool to evaluate the CTE properties. It is clearly seen that the coefficient is not linear but varies with temperature. To maintain the temperature in MD, thermostats are used and there... Show moreThe Coefficient of Thermal Expansion (CTE) of Carbon nanotubes (CNTs) is determined using Molecular Dynamics (MD) simulations. Accurately evaluating CTE using experimental methods still suffers from size restrictions and measurement limitations. Thus, computational methods (MD simulations) prove to be an ideal tool to evaluate the CTE properties. It is clearly seen that the coefficient is not linear but varies with temperature. To maintain the temperature in MD, thermostats are used and there are different types of thermostats available in an MD code. The effect of various parameters on the performance of each of the thermostats and whether they are capable of representing the physics of the problem are examined. The key numerical parameters and the effect of these parameters on the thermal and the thermo-mechanical properties are examined using MD simulations. It is found that many parameters affect the final results in the computation of CTE. However, MD is still capable of computing CTE as a function of temperature. Show less

Date Issued

2005

Identifier

FSU_migr_etd-2738

Format

Thesis

Title

Development and Characterization of High Strength Nb₃Sn Superconductor.

Out of the two most used materials (Nb3Sn and NbTi) for superconducting magnets, the Nb3Sn type conductor has been shown to have higher critical properties and capable to generate fields higher than 8 tesla. However, the superconducting properties of Nb3Sn are highly strain sensitive and mechanically weak. To fully utilize the high critical current of Nb3Sn conductor, strengthened Nb3Sn wires are required. In this research a review and comparison of various approaches to strengthen Nb3Sn... Show moreOut of the two most used materials (Nb3Sn and NbTi) for superconducting magnets, the Nb3Sn type conductor has been shown to have higher critical properties and capable to generate fields higher than 8 tesla. However, the superconducting properties of Nb3Sn are highly strain sensitive and mechanically weak. To fully utilize the high critical current of Nb3Sn conductor, strengthened Nb3Sn wires are required. In this research a review and comparison of various approaches to strengthen Nb3Sn supperconductors have been carried out. The dispersion strengthening approach was selected as a major strengthening method. Here, a detailed study on the fabrication and characterization of alumina nanoparticle dispersion strengthened Nb3Sn wires is presented. Both the mechanical and superconducting properties were concurrently improved by using this method. To rationalize and select the strengthening approach, stress-strain analysis was carried out. The calculation of the final strength of the composite conductors considers (1) Thermal strain due to the cooling from high temperature to 4 K and, (2) Internal stress/strain due to the shape and distribution of the Nb3Sn filaments in the conductors. A 1D model was developed to calculate the thermal prestrain and predict the performance of composite wire. The results from 1D model were helpful for understanding the influence of thermal stress on mechanical properties. Furthermore, a 3D model was also developed based on the basic Micromechanics theory. The 3D model provided more insights on the relationship between internal stress-strain state and external loads, such as temperature drop and applied tensile or compressive stresses. Because Nb3Sn's performances are highly strain sensitive, especially for high field applications, the study of stress-strain state has significant meanings for improving fabrication process and optimizing the design of the Nb3Sn superconductors. Based on the calculations and literature survey, the fabrication and strengthening approaches were selected and optimized. Modified cable-in-tube (MCIT) process was used as the major fabrication method, because this process has characteristics of simplicity and short fabrication cycle. Moreover, it is capable of dealing with high strength materials and varied designs. Therefore this process is suitable for developing new composite materials and optimizing process parameters. Nanoparticle strengthened Cu (DSC) was used as a precursor. The formability of DSC/Nb combination and DSC/Sn combination were carefully investigated. The bonding between Cu and Cu was also investigated in order to avoid defects related to incomplete bonding. Heat treatment conditions were also studied systematically. Based on all these preliminary investigations, alumina nanoparticle reinforced Nb3Sn wire was fabricated using MCIT process. Microstructure characterization, tensile tests and critical current ~ strain measurements were carried out to compare the newly developed Nb3Sn and the regular wire fabricated by exactly the same procedures. The experimental results were consistent with the calculation. The developed wire showed improvement in both the critical current and mechanical strength. Show less

Date Issued

2006

Identifier

FSU_migr_etd-3855

Format

Thesis

Title

Development of a Dynamic Bipedal Climbing and Multi-Modal Robotic Platform.

Animals often exhibit the ability to operate in and transition between multiple modes of locomotion efficiently and elegantly. On the other hand, robotic platforms have typically focused on a single mode of locomotion. This thesis presents the conceptual development, design, and verification of a robotic platform capable of locomotion in scansorial and aerial regimes based on biological analogs. A review of related work is conducted on animals, previous climbing platforms, and multi-modal... Show moreAnimals often exhibit the ability to operate in and transition between multiple modes of locomotion efficiently and elegantly. On the other hand, robotic platforms have typically focused on a single mode of locomotion. This thesis presents the conceptual development, design, and verification of a robotic platform capable of locomotion in scansorial and aerial regimes based on biological analogs. A review of related work is conducted on animals, previous climbing platforms, and multi-modal robots. A 2D dynamics simulation is developed and the effect of sprawl angle simulated. The development of a miniature bipedal dynamic climbing platform is discussed and an experimental investigation on the effect of sprawl angle on dynamic climbing conducted. The platform design for a multi-modal climbing and gliding robot is presented and a discussion on the trade-offs for multi-modal locomotion presented. The multi-modal platform, ICAROS, is experimentally operated to verify the design specifications. The resulting ICAROS platform demonstrates climbing prepared vertical surfaces and transitioning to a glide path with performance characteristics comparable to its biological counterparts. Show less

Date Issued

2012

Identifier

FSU_migr_etd-4798

Format

Thesis

Title

Development of a Framework for Charging Energy Storage for Large-Nonlinear Loads in a Tightly Coupled Microgrid Power System.

Tightly coupled microgrid power systems strike a balance between maintaining the desired power quality and insuring a high utilization efficiency of large-nonlinear loads. This is of great interest to the US Navy. Application of large-nonlinear loads in microgrid power systems requires energy storage to serve as the power supply for the large-nonlinear load. Degradation of power quality caused by improper charging large-nonlinear load's energy storage will affect the normal operation of every... Show moreTightly coupled microgrid power systems strike a balance between maintaining the desired power quality and insuring a high utilization efficiency of large-nonlinear loads. This is of great interest to the US Navy. Application of large-nonlinear loads in microgrid power systems requires energy storage to serve as the power supply for the large-nonlinear load. Degradation of power quality caused by improper charging large-nonlinear load's energy storage will affect the normal operation of every electrical device inside it. The objectives of the proposed generalized framework for charging energy storage for large-nonlinear loads in a tightly coupled microgrid are to 1) mitigate the power impact of energy storage charging in order to maintain the desired power quality in microgrid power systems. and 2)ensure a rapid charging speed of the energy storage. In this research, the aforementioned objectives were pursued using both hardware and software solutions. The hardware solution involved selecting an optimal distribution architecture that can ensure fast charging of energy storage without degradation of power quality. The software solution involved the development of a comprehensive control strategy that can coordinate power generation controls and energy storage charging. The goal of developing a generalized microgrid scale framework for charging an energy storage for large-nonlinear load module was thus achieved. This achievement can contribute to the application of large-nonlinear loads in tightly coupled microgrid power systems. Show less